OBD2 Live Data Values: A Comprehensive Guide for Automotive Diagnostics

Understanding Obd2 Live Data Values is crucial for anyone involved in automotive diagnostics and repair. Modern vehicles are equipped with sophisticated onboard diagnostic systems that constantly monitor a vast array of parameters, providing real-time insights into the engine’s performance and overall vehicle health. This article serves as an in-depth guide to these data points, commonly known as Parameter Identifiers (PIDs), offering a detailed explanation of their meaning and significance for effective car troubleshooting.

This comprehensive resource is designed to empower both professional mechanics and car enthusiasts with the knowledge to interpret OBD2 live data values accurately. By understanding these parameters, you can gain a deeper understanding of your vehicle’s operation, identify potential issues, and perform more precise and efficient repairs.

Decoding Vehicle Operation Parameters

The following section details the OBD2 live data values related to general vehicle operation. These parameters provide fundamental information about the engine’s running condition and the vehicle’s motion.

Engine RPM (Revolutions Per Minute)

Engine RPM, or Revolutions Per Minute, indicates how fast the engine’s crankshaft is rotating. This obd2 live data value is a fundamental measure of engine speed and is crucial for assessing engine performance under various conditions. Higher RPM generally corresponds to increased engine power output.

• Normal Range: Varies significantly depending on vehicle type, engine size, and operating condition. Idle RPM typically ranges from 600-1000 RPM. During acceleration, RPM can climb significantly higher.
• Diagnostic Significance:
  • High Idle RPM: Could indicate vacuum leaks, throttle body issues, or problems with the idle air control system.
  • Low Idle RPM: Might suggest issues with fuel delivery, ignition, or engine compression.
  • Erratic RPM: Can point to problems with the engine’s control system, sensor malfunctions, or misfires.

Vehicle Speed

Vehicle Speed is a straightforward obd2 live data value that reports the current speed of the vehicle, usually in miles per hour (MPH) or kilometers per hour (KPH). This parameter is essential for verifying speedometer accuracy and diagnosing speed-related issues.

• Normal Range: Directly reflects the vehicle’s actual speed.
• Diagnostic Significance:
  • Speedometer Discrepancies: Comparing the OBD2 speed reading with the speedometer reading can help identify issues with the speedometer cluster or vehicle speed sensor.
  • Transmission Problems: Inconsistent or erratic speed readings might be related to transmission sensor failures or internal transmission problems.
  • ABS/Traction Control Issues: Speed data is used by ABS and traction control systems. Incorrect readings can lead to malfunctions in these systems.

Engine Coolant Temperature

Engine Coolant Temperature is a critical obd2 live data value that reflects the temperature of the engine coolant. Monitored by a coolant temperature sensor, this parameter is vital for preventing engine overheating and ensuring efficient engine operation.

• Normal Range: Typically between 195°F to 220°F (90°C to 104°C) under normal operating conditions, but can vary slightly between vehicles.
• Diagnostic Significance:
  • Overheating: High coolant temperature readings indicate potential overheating issues, which could be caused by a faulty thermostat, radiator problems, coolant leaks, or a failing water pump.
  • Cold Running Engine: Low coolant temperature may suggest a stuck-open thermostat, leading to reduced engine efficiency and potential emissions problems.
  • Sensor Malfunction: Erratic or illogical readings can point to a faulty coolant temperature sensor.

Engine Oil Temperature

Engine Oil Temperature, measured by sensors like thermocouples or thermistors, is another important obd2 live data value. Maintaining optimal oil temperature is crucial for proper lubrication and preventing engine wear.

• Normal Range: Generally ranges from 200°F to 250°F (93°C to 121°C) under normal driving conditions, but can be higher under heavy load or hot weather.
• Diagnostic Significance:
  • Overheating Oil: High oil temperature can indicate excessive engine load, inadequate cooling, or oil degradation, potentially leading to engine damage.
  • Insufficient Oil Temperature: In cold climates or short trips, oil may not reach optimal temperature, reducing lubrication effectiveness.
  • Sensor Issues: Inaccurate readings can be due to a faulty oil temperature sensor.

Ambient Air Temperature

Ambient Air Temperature is the temperature of the air outside the vehicle, measured by a sensor typically located near the front bumper. This obd2 live data value is used by the engine control unit (ECU) to adjust fuel and ignition parameters for optimal performance in varying weather conditions.

• Normal Range: Reflects the actual outside air temperature.
• Diagnostic Significance:
  • Sensor Accuracy: Comparing this reading with local weather forecasts can help verify sensor accuracy.
  • Climate Control Issues: While primarily for engine management, significant discrepancies could indirectly point to issues with the climate control system’s sensors.
  • Engine Performance Problems: In rare cases, a drastically inaccurate ambient air temperature reading could affect engine performance calculations.

Barometric Pressure

Barometric Pressure, also known as Atmospheric Pressure, is measured by a BARO sensor. This obd2 live data value is used by the Powertrain Control Module (PCM) to adjust fuel trim and engine timing, as air density changes with altitude and atmospheric pressure.

• Normal Range: Average barometric pressure at sea level is approximately 14.7 PSI. Pressure decreases with altitude.
• Diagnostic Significance:
  • Altitude Compensation: The PCM uses this reading to adjust for altitude changes, ensuring proper air-fuel mixture.
  • Sensor Malfunction: Incorrect readings can lead to improper fuel trim and engine performance issues, especially at varying altitudes.
  • Vacuum Leaks: In some cases, unusually low barometric pressure readings might indirectly suggest significant vacuum leaks affecting manifold pressure.

Accelerator Pedal Position

Accelerator Pedal Position is a obd2 live data value that indicates the position of the accelerator pedal, reflecting the driver’s demand for engine power. It is measured by a sensor on the pedal assembly.

• Normal Range: Ranges from 0% (pedal released) to 100% (pedal fully depressed).
• Diagnostic Significance:
  • Throttle Response Issues: Discrepancies between pedal position and engine response can indicate problems with the throttle position sensor, throttle actuator, or electronic throttle control system.
  • Cruise Control Problems: Faulty accelerator pedal position sensor can affect cruise control operation.
  • Drive-by-Wire System Faults: This reading is crucial for diagnosing issues in drive-by-wire systems.

Relative Accelerator Pedal Position

Relative Accelerator Pedal Position is a calculated obd2 live data value that evaluates the pedal position based on sensor output voltages. It may not always show 100% when the pedal is fully depressed due to sensor calibration and system design.

• Normal Range: Similar to Accelerator Pedal Position but might have a slightly lower maximum value than 100%.
• Diagnostic Significance: Similar to Accelerator Pedal Position, focusing on sensor calibration and potential discrepancies in readings.

Commanded Throttle Actuator

Commanded Throttle Actuator represents the throttle position requested by the ECU based on the accelerator pedal position and other factors. This obd2 live data value reflects the ECU’s intended throttle opening.

• Normal Range: Ranges from closed to fully open, depending on driver input and engine control strategy.
• Diagnostic Significance:
  • Throttle Control Issues: Comparing commanded throttle position with actual throttle position (see below) is crucial for diagnosing throttle actuator problems, electronic throttle control malfunctions, or issues with the ECU’s control logic.
  • Performance Problems: If the commanded throttle position is not aligning with driver input or expected engine response, it can point to performance issues.

Relative Throttle Position

Relative Throttle Position compares the actual throttle position to a learned closed position. This obd2 live data value is important because carbon buildup or other factors can affect throttle body behavior over time. The system adjusts to compensate for these changes.

• Normal Range: Reflects the throttle opening relative to the learned closed position.
• Diagnostic Significance:
  • Carbon Buildup: Significant adjustments in relative throttle position over time can indicate carbon buildup in the throttle body, requiring cleaning.
  • Throttle Body Issues: Erratic or illogical readings can point to problems with the throttle position sensor or throttle body itself.

Absolute Throttle Position

Absolute Throttle Position, also known as the actual throttle position, is a direct measurement of the throttle valve opening. This obd2 live data value is typically expressed as a percentage, with 0% being fully closed and 100% being fully open.

• Normal Range: 0% to 100%, directly reflecting the physical throttle valve position.
• Diagnostic Significance:
  • Throttle Position Sensor (TPS) Issues: Inaccurate or erratic readings are a primary indicator of a faulty TPS.
  • Sticking Throttle: If the absolute throttle position doesn’t change smoothly with accelerator pedal input, it could indicate a sticking throttle valve.
  • Electronic Throttle Control Problems: This reading is essential for diagnosing electronic throttle control system malfunctions.

Control Module Voltage

Control Module Voltage represents the voltage supplied to the engine control unit (ECU). This obd2 live data value is a good indicator of the ECU’s power supply health and is typically close to the system voltage when the vehicle is running. It is important to note that this is not the same as battery voltage.

• Normal Range: Typically around 12-14.5 volts when the engine is running, similar to system voltage.
• Diagnostic Significance:
  • Low Voltage: Low control module voltage can indicate issues with the charging system (alternator, battery), wiring problems, or a failing ECU.
  • Voltage Fluctuations: Unstable voltage readings can cause various ECU malfunctions and sensor errors.
  • Power Supply Problems: This parameter helps diagnose power-related issues affecting the ECU’s operation.

Hybrid Battery Pack Remaining Life

Hybrid Battery Pack Remaining Life is a obd2 live data value specific to hybrid vehicles. It indicates the remaining charge percentage in the hybrid battery pack. Standard OBD2 typically does not show individual cell data.

• Normal Range: 0% to 100%, reflecting the state of charge of the hybrid battery.
• Diagnostic Significance:
  • Battery Health Monitoring: Provides a general indication of the hybrid battery’s state of charge and overall health.
  • Hybrid System Issues: Abnormal readings or rapid discharge can point to problems within the hybrid battery system or charging system.
  • Limitations: Standard OBD2 provides limited data; more detailed battery diagnostics require specialized hybrid scan tools.

Hybrid/EV Vehicle System Status

Hybrid/EV Vehicle System Status is a composite obd2 live data value providing information on various aspects of hybrid and electric vehicle systems. Parameters displayed may include:

• HEV Charging State:

  • Charge Sustaining Mode (CSM): System maintains a constant State of Charge.
  • Charge Depletion Mode (CDM): System targets lower State of Charge values.

• HEV Battery Voltage: Ranges from 0V to 1024V.

• HEV Battery Current: Ranges from -3300 Amps to 3300 Amps (negative value indicates charging).

• Normal Range: Varies significantly depending on the specific hybrid/EV system.

• Diagnostic Significance:

  • Charging System Diagnostics: Helps diagnose issues with the charging system, battery management system, and overall hybrid/EV system operation.
  • System Mode Identification: Indicates the current operating mode of the hybrid system (CSM or CDM).
  • High Voltage System Monitoring: Provides critical voltage and current data for high-voltage battery systems.

Calculated Engine Load Value

Calculated Engine Load Value is a obd2 live data value derived from the Mass Air Flow (MAF) sensor reading. It represents the current airflow in the engine as a percentage of the peak airflow, corrected for altitude.

• Normal Range: Varies depending on engine load. Lower at idle, higher during acceleration.
• Diagnostic Significance:
  • Engine Load Assessment: Provides an indication of how hard the engine is working.
  • MAF Sensor Performance: Used in conjunction with other MAF sensor readings to assess sensor accuracy and identify potential airflow restrictions.
  • Performance Issues: Abnormally high or low load values can indicate engine performance problems.

Absolute Load Value

Absolute Load Value is a normalized percentage value of air mass per intake stroke, calculated by dividing the air mass per intake stroke by the air mass per intake stroke at 100% throttle. This obd2 live data value offers another perspective on engine load.

• Normal Range: Similar to Calculated Engine Load Value, but values may differ at idle, during parking, or without accessories due to normalization.
• Diagnostic Significance: Similar to Calculated Engine Load Value, providing further insight into engine load and airflow characteristics.

Driver’s Demand Engine – Percent Torque

Driver’s Demand Engine – Percent Torque is a obd2 live data value representing the maximum available engine torque percentage requested by the driver based on accelerator pedal position, cruise control settings, and transmission demands. It is determined by the ECU.

• Normal Range: 0% to 100%, reflecting the driver’s torque request.
• Diagnostic Significance:
  • Torque Delivery Issues: Discrepancies between driver’s demand torque and actual engine torque can indicate problems with engine performance, transmission control, or electronic control systems.
  • Cruise Control Diagnostics: Helps diagnose torque-related issues during cruise control operation.

Actual Engine – Percent Torque

Actual Engine – Percent Torque, also known as Indicated Torque, represents the current percentage of the total available engine torque. This obd2 live data value considers net brake torque and friction torque required to run the engine without load.

• Normal Range: Varies depending on engine operating conditions and load.
• Diagnostic Significance:
  • Engine Performance Analysis: Provides a direct measure of the engine’s current torque output.
  • Torque Converter Issues: Abnormal torque readings can be related to torque converter problems in automatic transmissions.
  • Engine Mechanical Problems: In some cases, significant torque deviations can indicate engine mechanical issues.

Engine Friction – Percent Torque

Engine Friction – Percent Torque is the percentage of maximum engine torque required to overcome internal engine friction and run a “fully equipped” no-load engine. This obd2 live data value accounts for components like internal engine parts, fuel, water pump, air intake, alternator, exhaust, and emission control equipment.

• Normal Range: Relatively consistent for a given engine design, but can vary slightly with engine temperature and wear.
• Diagnostic Significance:
  • Engine Mechanical Condition: Increased friction torque over time might suggest increased engine wear or mechanical problems.
  • Baseline for Torque Calculations: Provides a baseline for understanding engine torque losses due to friction.

Engine Reference Torque

Engine Reference Torque is a fixed torque rating of the engine, considered as 100% for Actual Engine Percentage Torque and other parameters using percentage torque outputs. This obd2 live data value remains constant and never changes over time.

• Normal Range: A fixed value specific to the engine model.
• Diagnostic Significance:
  • Reference Point: Serves as a constant reference point for interpreting percentage-based torque parameters.
  • Engine Identification: Can be used to verify engine specifications and identification.

Engine Percent Torque Data

Engine Percent Torque Data is a parameter used when changes in vehicle conditions can cause the torque reference to change. This obd2 live data value acknowledges that the 100% torque reference point may not always be constant.

• Normal Range: Varies depending on vehicle and engine conditions.
• Diagnostic Significance:
  • Dynamic Torque Reference: Indicates when the torque reference point is dynamically adjusted by the system.
  • Advanced Torque Management: Reflects more sophisticated torque management strategies in modern vehicles.

Auxiliary Input/Output

Auxiliary Input/Output is a composite obd2 live data value capable of providing details on various vehicle system statuses, including:

• Power Take Off (PTO) Status: On or Off.

• Glow Plug Lamp Status: On or Off.

• Automatic Transmission Status: Park/Neutral or Drive/Reverse.

• Manual Transmission Status: Neutral/Clutch In or In Gear.

• Recommended Transmission Gear: 1 to 15.

• Normal Range: Discrete values representing different system states.

• Diagnostic Significance:

  • Transmission System Monitoring: Provides status information for both automatic and manual transmissions.
  • Accessory System Status: Indicates the status of auxiliary systems like PTO and glow plugs.
  • System Mode Verification: Helps verify the correct operational mode of various vehicle systems.

Exhaust Gas Temperature (EGT)

Exhaust Gas Temperature (EGT) is a critical obd2 live data value measured by sensors installed in the exhaust system to protect components from overheating. EGT sensors may be located at:

• Turbocharger (Pre- and Post-Turbo)

• Catalytic Converter (Pre- and Post-Cat)

• Diesel Particulate Filter (DPF)

• NOx Reduction System Components

• Normal Range: Varies greatly depending on sensor location and engine operating conditions. Turbocharger EGTs can be significantly higher than catalytic converter EGTs.

• Diagnostic Significance:

  • Overheating Protection: High EGT readings can indicate potential overheating of critical exhaust components, which could be caused by engine problems, exhaust restrictions, or malfunctioning emission control systems.
  • Turbocharger Health: EGT readings are vital for monitoring turbocharger health and identifying potential issues.
  • Catalytic Converter Efficiency: EGT data helps assess catalytic converter performance.
  • DPF Regeneration Monitoring: EGT spikes are expected during DPF regeneration cycles.

Engine Exhaust Flow Rate

Engine Exhaust Flow Rate is a calculated obd2 live data value representing the flow rate of the air and fuel mixture ignited in the engine. Calculation requires exhaust temperature, volumetric efficiency, engine size, and flywheel RPM.

• Normal Range: Varies significantly with engine speed and load.
• Diagnostic Significance:
  • Airflow Analysis: Provides insights into engine airflow characteristics.
  • Performance Diagnostics: Abnormal exhaust flow rates can indicate engine performance problems or exhaust restrictions.
  • Emissions System Monitoring: Used in conjunction with other data to assess emissions system performance.

Exhaust Pressure

Exhaust Pressure is displayed as an absolute pressure value when the engine is running and roughly ambient atmospheric value when it is off. This obd2 live data value can report data from one or two exhausts depending on vehicle configuration.

• Normal Range: Slightly above atmospheric pressure when the engine is running.
• Diagnostic Significance:
  • Exhaust System Restrictions: High exhaust pressure readings can indicate restrictions in the exhaust system, such as a clogged catalytic converter or muffler.
  • Engine Performance Issues: Excessive backpressure can negatively impact engine performance.

Manifold Surface Temperature

Manifold Surface Temperature is the temperature value of the exhaust manifold’s outer surface. This obd2 live data value provides another temperature reading in the exhaust system.

• Normal Range: Lower than EGT readings but still indicative of exhaust system temperature.
• Diagnostic Significance: Similar to EGT, but less direct measure of internal exhaust gas temperature. Can still indicate overheating or exhaust system issues.

Timing Advance for #1 Cylinder

Timing Advance for #1 Cylinder is a manufacturer-specific obd2 live data value indicating the angle of the top dead center (TDC) and the time before the #1 cylinder should fire.

• Normal Range: Varies depending on engine operating conditions and engine control strategy.
• Diagnostic Significance:
  • Ignition Timing Issues: Abnormal timing advance values can indicate problems with the ignition system, timing control, or crankshaft/camshaft position sensors.
  • Engine Performance Problems: Incorrect timing advance can lead to misfires, reduced power, and poor fuel economy.
  • Knock Sensor Activity: The ECU adjusts timing advance based on knock sensor feedback to prevent engine knocking.

Engine Run Time

Engine Run Time is a composite obd2 live data value reporting the total run time of the engine in various states:

• Engine Run Time in Seconds: Total engine run time.

• Engine Idle Time In Seconds: Total time spent idling.

• Engine Run Time when PTO is engaged: Run time with Power Take-Off engaged.

• Normal Range: Continuously increasing values as the engine runs.

• Diagnostic Significance:

  • Engine Usage Tracking: Provides a record of engine operating hours.
  • Service Interval Tracking: Can be used to track engine run time for maintenance scheduling.
  • Idle Time Analysis: Excessive idle time can indicate certain driving patterns or operational issues.

Run Time Since Engine Start

Run Time Since Engine Start is a obd2 live data value representing the total run time in seconds since the engine was last started.

• Normal Range: Resets to zero with each engine start and increases continuously until the engine is shut off.
• Diagnostic Significance:
  • Trip Duration: Simple measure of the current trip duration.
  • Short Trip Detection: Can be used to identify frequent short trips, which can be detrimental to engine health in some cases.

Time Run with MIL On

Time Run with MIL On is the total engine run time since the Malfunction Indicator Lamp (MIL), or check engine light, was activated after a Diagnostic Trouble Code (DTC) was set. This obd2 live data value is distinct from total elapsed time.

• Normal Range: Starts counting when the MIL is activated and continues to increase as long as the MIL remains on.
• Diagnostic Significance:
  • DTC History: Indicates how long the vehicle has been driven with an active fault.
  • Intermittent Fault Analysis: Helps assess the duration of intermittent faults.

Distance Traveled while MIL is Activated

Distance Traveled while MIL is Activated is the total distance the vehicle has traveled since the check engine light activation. This obd2 live data value resets when codes are cleared or the battery is disconnected.

• Normal Range: Starts counting when the MIL is activated and increases with vehicle mileage as long as the MIL remains on.
• Diagnostic Significance:
  • DTC Severity Assessment: Indicates how much the vehicle has been driven with an active fault, potentially reflecting the severity or persistence of the issue.

Time since Trouble Codes Cleared

Time since Trouble Codes Cleared is the total engine run time since DTCs were last cleared using an OBD2 scan tool or by disconnecting the battery. This obd2 live data value helps track the time elapsed since the last code clearing event.

• Normal Range: Starts at zero after code clearing and increases with engine run time.
• Diagnostic Significance:
  • Post-Repair Monitoring: Used to monitor if codes reappear after repairs.
  • Troubleshooting History: Helps track the frequency of code clearing and potential recurring issues.

Distance Traveled Since Codes Cleared

Distance Traveled Since Codes Cleared is the total distance covered by the vehicle since DTCs were cleared. This obd2 live data value does not reset even when non-engine codes are cleared.

• Normal Range: Starts at zero after code clearing and increases with vehicle mileage.
• Diagnostic Significance: Similar to Time since Trouble Codes Cleared, providing mileage-based tracking since the last code clearing event.

Warm-ups Since Codes Cleared

Warm-ups Since Codes Cleared is the total number of engine warm-up cycles completed after clearing codes or disconnecting the battery. A warm-up cycle is defined as when the coolant temperature reaches at least 40°F after startup and then reaches at least 170°F. This obd2 live data value tracks warm-up cycles since the last code reset.

• Normal Range: Increments with each completed warm-up cycle.
• Diagnostic Significance:
  • Drive Cycle Monitoring: Tracks drive cycles, which are important for emissions testing and verifying repairs.
  • Intermittent Fault Triggering: Some intermittent faults may only appear after a certain number of warm-up cycles.

Fuel & Air Parameters: Monitoring Engine Combustion

This section focuses on obd2 live data values related to the fuel and air systems, which are critical for proper engine combustion and efficiency.

Fuel System Status

Fuel System Status is a obd2 live data value that indicates the operating mode of the fuel system, typically displaying status for two fuel systems if applicable. Common modes include:

• Open Loop Mode: The ECU uses pre-programmed air-fuel ratios without feedback from oxygen sensors.

• Closed Loop Mode: The ECU uses oxygen sensor feedback to adjust the air-fuel ratio for optimal combustion.

• Normal Range: Switches between Open and Closed Loop depending on engine temperature, load, and operating conditions. Closed loop is generally the target mode for optimal efficiency and emissions control during normal operation.

• Diagnostic Significance:

  • Open Loop Under Normal Conditions: Indicates potential issues with oxygen sensors, engine temperature sensors, or other components preventing the system from entering closed loop.
  • Fuel Trim Issues: Fuel trim values (see below) are closely related to fuel system status and are interpreted differently in open and closed loop modes.

Oxygen Sensor Voltage

Oxygen Sensor Voltage is a obd2 live data value measuring the voltage generated by the oxygen sensor (O2 sensor). This voltage reflects the oxygen content in the exhaust gas, indicating the air-fuel mixture ratio.

• Normal Range: Typically fluctuates between 0.1V and 0.9V for standard narrowband O2 sensors in closed loop operation. Around 0.45V represents stoichiometric mixture. Wideband sensors have different voltage ranges.
• Diagnostic Significance:
  • Lean Mixture: Low voltage (closer to 0.1V) indicates a lean mixture (excess air).
  • Rich Mixture: High voltage (closer to 0.9V) indicates a rich mixture (excess fuel).
  • Sensor Response: Slow or sluggish sensor response can indicate a failing O2 sensor.
  • Circuit Problems: Fixed voltage readings (stuck high or low) can point to sensor or wiring issues.

Oxygen Sensor Equivalence Ratio (Lambda)

Oxygen Sensor Equivalence Ratio, also known as Lambda, is another obd2 live data value related to oxygen sensor readings. In closed loop mode, this sensor provides feedback to the ECU to adjust the air-fuel mixture. In open loop mode, the ECU does not use this feedback.

• Normal Range: Ideally around 1.0 in closed loop for stoichiometric mixture. Values less than 1.0 indicate a rich mixture, and values greater than 1.0 indicate a lean mixture.
• Diagnostic Significance: Similar to Oxygen Sensor Voltage, providing a normalized representation of the air-fuel mixture ratio based on O2 sensor readings.

Oxygen Sensor Current

Oxygen Sensor Current is the current flowing within the oxygen sensor. This obd2 live data value provides information about the air-fuel mixture based on current flow in the sensor circuit.

• Normal Range: 0 mA indicates a balanced air-fuel ratio (stoichiometric). Positive current indicates a lean mixture, and negative current indicates a rich mixture.
• Diagnostic Significance: Provides another perspective on air-fuel mixture, particularly useful for diagnosing sensor biases or circuit issues.

Short Term Fuel Trim (STFT)

Short Term Fuel Trim (STFT) is a obd2 live data value representing immediate, short-term adjustments made by the ECU to the air-fuel mixture in response to oxygen sensor feedback.

• Normal Range: Ideally close to 0%. Values typically fluctuate within a range of -10% to +10%.
• Diagnostic Significance:
  • Fuel Mixture Corrections: Indicates the ECU’s immediate attempts to correct lean or rich conditions.
  • Lean Condition (Positive STFT): Positive values indicate the ECU is adding fuel to compensate for a lean mixture, which could be caused by vacuum leaks, low fuel pressure, or lean-running injectors.
  • Rich Condition (Negative STFT): Negative values indicate the ECU is reducing fuel to compensate for a rich mixture, which could be caused by high fuel pressure, leaking injectors, or a rich bias in sensor readings.
  • Excessive Trim Values: Consistently high positive or negative STFT values, especially combined with LTFT (see below), indicate underlying fuel mixture problems requiring further investigation.

Long Term Fuel Trim (LTFT)

Long Term Fuel Trim (LTFT) is a obd2 live data value representing cumulative, long-term adjustments made by the ECU to the air-fuel mixture. These adjustments compensate for gradual changes and wear over time. LTFT values update relatively slowly (seconds) and are stored in the ECU’s memory.

• Normal Range: Ideally close to 0%. Values typically fluctuate within a range of -10% to +10%.
• Diagnostic Significance:
  • Long-Term Fuel Mixture Adaptations: Reflects the ECU’s learned corrections for consistent lean or rich conditions over time.
  • Vacuum Leaks (Positive LTFT): Positive LTFT, especially combined with positive STFT, often indicates vacuum leaks.
  • Fuel Delivery Issues (Positive LTFT): Can also indicate low fuel pressure, clogged fuel filter, or weak fuel pump.
  • Injector Problems (Negative LTFT): Negative LTFT, especially combined with negative STFT, can indicate leaking fuel injectors.
  • MAF Sensor Issues (Positive or Negative LTFT): MAF sensor inaccuracies can lead to both lean and rich conditions and affect fuel trim values.
  • Catalytic Converter Efficiency Issues: In some cases, LTFT can be affected by catalytic converter efficiency problems.

Commanded Equivalence Ratio (CER)

Commanded Equivalence Ratio (CER), also known as lambda, is a obd2 live data value that determines the air-fuel ratio requested by the ECU.

• Normal Range:
  • Wide Range O2 Sensor Vehicles: CER is displayed in both open and closed loop modes, ideally around 1.0 for stoichiometric mixture.
  • Conventional O2 Sensor Vehicles: CER is displayed in open loop mode. In closed loop mode, it typically displays 1.0.
• Diagnostic Significance: Indicates the ECU’s target air-fuel ratio. Deviations from expected values can point to ECU control issues or sensor disagreements.

Mass Air Flow Rate (MAF)

Mass Air Flow Rate (MAF) is a obd2 live data value measured by the MAF sensor, representing the amount of air entering the engine intake system.

• Normal Range: Varies significantly with engine size and operating conditions. At idle, typically ranges from 2 to 7 g/s. At 2500 RPM, it should increase to between 15 to 25 g/s. Consult manufacturer specifications for specific vehicle values.
• Diagnostic Significance:
  • MAF Sensor Malfunction: Incorrect or erratic MAF readings are common indicators of a faulty MAF sensor.
  • Airflow Restrictions: Low MAF readings can indicate air intake restrictions, such as a clogged air filter or intake blockage.
  • Vacuum Leaks (Indirectly): While MAF directly measures intake air, large vacuum leaks can sometimes affect MAF readings.
  • Engine Performance Issues: Inaccurate MAF readings can lead to incorrect air-fuel mixture, resulting in poor engine performance, misfires, and emissions problems.

Intake Air Temperature (IAT)

Intake Air Temperature (IAT) is a obd2 live data value representing the temperature of the air entering the engine cylinders. Vehicles may have multiple IAT sensors for different purposes:

• Measuring air entering the engine.

• Measuring climate control system air.

• Measuring ambient air temperature (sometimes shared with ambient air temp sensor).

• Normal Range: Should generally reflect the temperature of the air entering the intake system, typically warmer than ambient air due to engine heat.

• Diagnostic Significance:

  • IAT Sensor Malfunction: Incorrect or illogical IAT readings can indicate a faulty IAT sensor.
  • Engine Performance Issues: Incorrect IAT readings can affect air density calculations and lead to improper air-fuel mixture adjustments.
  • Turbocharger/Supercharger Efficiency: Post-turbocharger IAT readings are important for assessing intercooler efficiency.

Intake Manifold Absolute Pressure (MAP)

Intake Manifold Absolute Pressure (MAP) is a obd2 live data value measured by the MAP sensor in the intake manifold. It reflects the absolute pressure within the manifold.

• Normal Range:
  • Running Engine: 18-20 “Hg vacuum (lower absolute pressure).
  • Idle Engine: 0-20 “Hg vacuum (lower absolute pressure).
  • Key On Engine Off (KOEO): Should be close to barometric pressure.
• Diagnostic Significance:
  • Vacuum Leaks: Higher than expected MAP readings (lower vacuum) at idle or during deceleration are strong indicators of vacuum leaks.
  • MAP Sensor Malfunction: Incorrect or erratic MAP readings can point to a faulty MAP sensor.
  • Engine Performance Problems: MAP sensor data is crucial for fuel and ignition calculations. Incorrect readings can lead to various engine performance issues.
  • Boost Pressure Indication (Turbocharged Engines): In turbocharged engines, MAP readings above atmospheric pressure indicate boost.

Fuel Pressure (Gauge)

Fuel Pressure (Gauge) is a obd2 live data value representing the fuel pressure in the fuel system, displayed as a gauge pressure value. A gauge pressure of 0 indicates atmospheric/ambient pressure.

• Normal Range: Varies significantly depending on vehicle type and fuel system design. Consult manufacturer specifications for your vehicle’s fuel pressure.
• Diagnostic Significance:
  • Low Fuel Pressure: Low fuel pressure can cause lean running conditions, misfires, and performance problems. Potential causes include a weak fuel pump, clogged fuel filter, or fuel pressure regulator issues.
  • High Fuel Pressure: High fuel pressure can cause rich running conditions and potential fuel leaks. Potential causes include a faulty fuel pressure regulator.
  • Fuel System Malfunctions: Erratic or unstable fuel pressure readings indicate fuel system problems.

Fuel Rail Pressure

Fuel Rail Pressure is another obd2 live data value representing fuel pressure in the fuel rail, also displayed as a gauge pressure value. 0 psi/kPa indicates atmospheric/ambient pressure.

• Normal Range: Similar to Fuel Pressure (Gauge), consult manufacturer specifications.
• Diagnostic Significance: Similar to Fuel Pressure (Gauge), providing fuel pressure readings specifically at the fuel rail.

Fuel Rail Pressure (Absolute)

Fuel Rail Pressure (Absolute) is a obd2 live data value representing fuel pressure in the fuel rail, but displayed as an absolute pressure value. When the fuel rail is not pressurized, this data point will display ambient pressure (approximately 14.7 psi or 101.3 kPa).

• Normal Range: Absolute pressure value of fuel rail pressure.
• Diagnostic Significance: Provides fuel rail pressure readings in absolute terms, which can be useful for certain diagnostic procedures and calculations.

Fuel Rail Pressure (Relative to Manifold Vacuum)

Fuel Rail Pressure (relative to manifold vacuum) is a obd2 live data value representing fuel pressure relative to the intake manifold vacuum.

• Normal Range: Varies depending on engine load and manifold vacuum.
• Diagnostic Significance: Provides fuel pressure data referenced to manifold vacuum, which can be relevant for diagnosing certain fuel system issues, especially in older systems with vacuum-referenced fuel pressure regulators.

Alcohol Fuel %

Alcohol Fuel % is a obd2 live data value representing the ethanol or alcohol content in the fuel, as measured by the engine computer in percentage. For example, E85 fuel would show approximately 85%.

• Normal Range: Depends on the fuel type being used. For regular gasoline (E10), it should be around 10%. For flex-fuel vehicles, it can vary widely depending on the fuel blend.
• Diagnostic Significance:
  • Fuel Composition Verification: Verifies the fuel composition being used, especially important for flex-fuel vehicles.
  • Fuel Sensor Issues: Incorrect readings can indicate a faulty fuel composition sensor.
  • Flex-Fuel System Problems: Helps diagnose issues in flex-fuel systems.

Fuel Level Input

Fuel Level Input is a obd2 live data value representing the percentage of maximum fuel tank capacity remaining.

• Normal Range: 0% to 100%, reflecting the fuel level in the tank.
• Diagnostic Significance:
  • Fuel Gauge Verification: Can be used to compare with the fuel gauge reading and identify potential fuel gauge inaccuracies.
  • Fuel Level Sensor Issues: Incorrect or erratic readings can point to a faulty fuel level sensor.

Engine Fuel Rate

Engine Fuel Rate is a obd2 live data value representing the near-instantaneous fuel consumption rate, expressed in Liters or Gallons per hour. It is calculated by the ECU using the volume of fuel used during the last 1000 ms (1 second). Note: This rate does not include fuel consumed by diesel aftertreatment systems.

• Normal Range: Varies significantly depending on engine load and RPM. Higher fuel rate during acceleration, lower at idle.
• Diagnostic Significance:
  • Fuel Consumption Monitoring: Provides real-time fuel consumption data.
  • Fuel Economy Analysis: Can be used to estimate fuel economy under different driving conditions.
  • Engine Efficiency Assessment: Abnormally high fuel rates for a given load can indicate engine inefficiency or fuel leaks.

Cylinder Fuel Rate

Cylinder Fuel Rate is a obd2 live data value representing the calculated amount of fuel injected per cylinder during the most recent intake stroke, displayed in mg/stroke.

• Normal Range: Varies depending on engine load and RPM.
• Diagnostic Significance:
  • Fuel Distribution Analysis: Provides insights into fuel distribution across cylinders.
  • Injector Performance (Potentially): While not directly measuring injector performance, significant imbalances between cylinders could indirectly suggest injector issues.

Fuel System Percentage Use

Fuel System Percentage Use is a obd2 live data value displaying the percentage of total fuel usage for each cylinder bank (up to four banks). It can also display data for two separate fuel systems (e.g., diesel & CNG) if supported by the vehicle.

• Normal Range: Percentages representing fuel usage distribution across banks.
• Diagnostic Significance:
  • Fuel Bank Imbalances: Identifies imbalances in fuel usage between engine banks, which could indicate issues with fuel delivery to specific banks.
  • Dual Fuel System Monitoring: Provides data for vehicles with dual fuel systems.

Fuel Injection Timing

Fuel Injection Timing is a obd2 live data value representing the angle (in degrees) of crankshaft rotation before top dead center (BTDC) at which the fuel injector begins to operate.

• Normal Range: Varies depending on engine load, RPM, and engine control strategy.
• Diagnostic Significance:
  • Injection Timing Issues: Abnormal injection timing values can indicate problems with the engine control system, crankshaft/camshaft position sensors, or fuel injection control.
  • Engine Performance Problems: Incorrect injection timing can lead to poor combustion, reduced power, and emissions problems.

Fuel System Control

Fuel System Control is a obd2 live data value providing status information for diesel vehicle fuel systems (for fuel systems 1 & 2 if supported), including:

• Fuel pressure control: Closed or open loop.
• Fuel injection quantity: Closed or open loop.
• Fuel injection timing: Closed or open loop.
• Idle fuel balance/contribution: Closed or open loop.

Closed loop indicates the system is using sensor feedback for fine-tuning. Systems 1 & 2 refer to two separate fuel systems, with system 2 potentially not in use on many vehicles.

• Normal Range: Indicates the control loop status for various fuel system parameters.
• Diagnostic Significance:
  • Diesel Fuel System Diagnostics: Provides detailed status information for diesel fuel control systems.
  • Control Loop Issues: Identifying open loop operation when closed loop is expected can indicate sensor or control system problems.

Fuel Pressure Control System

Fuel Pressure Control System is a obd2 live data value providing data for up to two fuel rails, including:

• Commanded rail pressure.
• Actual rail pressure.
• Temperature.

Pressure is reported as gauge pressure, where 0 indicates rail pressure equal to atmospheric pressure.

• Normal Range: Varies depending on diesel fuel system design and operating conditions.
• Diagnostic Significance:
  • Diesel Fuel Pressure Control Issues: Discrepancies between commanded and actual rail pressure indicate fuel pressure control problems.
  • Fuel Pressure Sensor Malfunctions: Incorrect pressure readings can point to faulty fuel pressure sensors.
  • Fuel Rail Temperature Monitoring: Provides temperature data for fuel rails.

Injection Pressure Control System

Injection Pressure Control System is a obd2 live data value relevant to some diesel engines that use a high-pressure oil rail to control fuel injection pressure. This parameter may display:

• Commanded Control Pressure Rail A.
• Actual Pressure Rail A.
• Commanded Control Pressure Rail B.
• Actual Pressure Rail B.

The ICP sensor monitors pressure on the oil side of the fuel system.

• Normal Range: Varies depending on diesel engine type and operating conditions.
• Diagnostic Significance:
  • Diesel Injection Pressure Control Problems: Discrepancies between commanded and actual injection control pressure indicate issues with the injection pressure control system.
  • ICP Sensor Malfunctions: Incorrect pressure readings can point to faulty ICP sensors.
  • HEUI System Diagnostics: Specifically relevant for diagnosing Hydraulically actuated Electronically controlled Unit Injector (HEUI) systems.

Boost Pressure Control

Boost Pressure Control is a obd2 live data value providing data for turbocharged vehicles, potentially for one or two turbochargers, including:

• ECM commanded boost pressure.
• Actual boost pressure.

All data is reported in absolute pressure. For example, 24.7 psi absolute pressure is equivalent to 10 psi gauge pressure (10 lbs of boost). At idle before turbo spool-up, readings should be at or slightly below ambient pressure. This parameter also provides feedback on boost control system operating mode:

• Open Loop: No sensor feedback, no faults.

• Closed Loop: Using sensor feedback, no faults.

• Fault Present: Boost data unreliable.

• Normal Range: Boost pressure varies significantly with engine load and turbocharger design. At idle, should be near atmospheric pressure. During acceleration, can increase significantly depending on boost level.

• Diagnostic Significance:

  • Boost Leaks: Lower than expected boost pressure can indicate boost leaks in the intake system.
  • Turbocharger Problems: Low or no boost can indicate turbocharger malfunctions.
  • Boost Control System Issues: Discrepancies between commanded and actual boost pressure, or fault codes related to boost control, indicate problems with the boost control system (wastegate, boost solenoid, etc.).
  • Turbocharger Overboost: Excessively high boost pressure can be dangerous and may indicate boost control system failures.

Turbocharger RPM

Turbocharger RPM is a obd2 live data value measuring the turbine RPM of one or both turbos, depending on vehicle configuration.

• Normal Range: Varies widely depending on turbocharger design and engine load. Can reach very high RPMs (hundreds of thousands). The maximum reported value is 655,350 RPM.
• Diagnostic Significance:
  • Turbocharger Performance Monitoring: Provides a direct measure of turbocharger speed, indicating turbocharger activity and performance.
  • Turbocharger Lag Analysis: Helps assess turbocharger response time and lag.
  • Turbocharger Failure (Potentially): Unusual RPM readings or lack of RPM change with engine load could indicate turbocharger problems.

Turbocharger Temperature

Turbocharger Temperature is a obd2 live data value reporting temperature data for one or both turbochargers, including:

• Compressor inlet temperature: Air charge temperature before the turbo.
• Compressor outlet temperature: Air charge temperature at the turbo outlet (should be higher than inlet).
• Turbine inlet temperature: Exhaust temperature pre-turbo (very high).
• Turbine outlet temperature: Exhaust temperature post-turbo (still high).

Charge air temperature range: -40 to 215 °C. Exhaust temperature range: -40 to 6513.5 °C.

• Normal Range: Varies depending on turbocharger location, design, and engine load. Turbine inlet temperatures are significantly higher than compressor outlet temperatures.
• Diagnostic Significance:
  • Turbocharger Overheating: Excessively high turbine inlet temperatures indicate potential turbocharger overheating, which can be caused by engine problems, excessive boost, or turbocharger malfunctions.
  • Intercooler Efficiency Assessment: Comparing compressor outlet temperature and charge air cooler temperature (CACT) helps assess intercooler efficiency.
  • Turbocharger Health Monitoring: Temperature readings provide valuable insights into turbocharger thermal stress and health.

Turbocharger Compressor Inlet Pressure Sensor

Turbocharger Compressor Inlet Pressure Sensor is a obd2 live data value measuring pressure at the turbocharger inlet, for one or two turbos depending on configuration. It is an absolute pressure value. Approximately 14.7 psi / 101.3 kPa indicates atmospheric pressure.

• Normal Range: Should be close to atmospheric pressure under normal conditions.
• Diagnostic Significance:
  • Air Filter Restriction: Lower than atmospheric pressure readings can indicate a restricted air filter or blockage in the intake path before the turbocharger.
  • Pressure Sensor Accuracy: Verifies the pressure reading at the turbo inlet.

Variable Geometry Turbo (VGT) Control

Variable Geometry Turbo (VGT) Control is a obd2 live data value relevant to vehicles with VGTs. It displays data related to the position/orientation of vanes in the turbocharger, including:

• Commanded VGT Position: Vane position requested by the vehicle (0% = max bypass, 100% = max boost).

• Actual VGT Vane Position.

• VGT Control Status: Closed or Open Loop (with or without sensor feedback), Fault State (data unreliable).

• Normal Range: VGT position varies dynamically depending on engine load and speed to optimize turbocharger performance.

• Diagnostic Significance:

  • VGT Actuator Problems: Discrepancies between commanded and actual VGT position indicate issues with the VGT actuator or control system.
  • VGT Sticking/Binding: Erratic or sluggish VGT position changes can suggest VGT vane sticking or binding due to soot buildup.
  • Turbocharger Performance Issues: VGT malfunctions can lead to boost problems, poor engine performance, and emissions issues.

Wastegate Control

Wastegate Control is a obd2 live data value relevant to turbocharged vehicles with wastegates. It reports data for electronic wastegate systems (one or two depending on configuration), including:

• Commanded wastegate position: Requested by the controller (0% = fully closed, 100% = max bypass).

• Actual wastegate position.

• Normal Range: Wastegate position varies dynamically to control boost pressure.

• Diagnostic Significance:

  • Wastegate Actuator Problems: Discrepancies between commanded and actual wastegate position indicate issues with the wastegate actuator or control system.
  • Wastegate Sticking/Binding: Wastegate sticking or binding can lead to boost control problems.
  • Boost Control Issues: Wastegate malfunctions can cause overboost or underboost conditions.

Charge Air Cooler Temperature (CACT)

Charge Air Cooler Temperature (CACT) is a obd2 live data value reporting the temperature of the intercooler air charge on turbocharged vehicles. Up to four sensors may be reported:

• Bank 1 Sensor 1.
• Bank 1 Sensor 2.
• Bank 2 Sensor 1.
• Bank 2 Sensor 2.

SAE/OBDII standard does not specify default mapping; factory manual may be needed for sensor location details.

• Normal Range: CACT should be significantly lower than compressor outlet temperature, indicating effective intercooler cooling.
• Diagnostic Significance:
  • Intercooler Inefficiency: High CACT readings indicate intercooler inefficiency, which can be caused by intercooler damage, blockage, or reduced airflow.
  • Boost Pressure Issues (Indirectly): Inefficient intercooling can lead to reduced boost pressure and engine performance.
  • Turbocharger Overheating (Indirectly): High CACT can contribute to increased turbocharger thermal stress.

Emissions Control Parameters: Monitoring Exhaust Aftertreatment

This section focuses on obd2 live data values related to emissions control systems, which are essential for reducing harmful pollutants in vehicle exhaust.

Commanded EGR

Commanded EGR is a obd2 live data value representing how open the Exhaust Gas Recirculation (EGR) valve should be, as requested by the engine computer. 0% is fully closed, 100% is fully open.

• Normal Range: EGR valve opening varies depending on engine load, speed, and temperature. EGR is typically active at part-load conditions to reduce NOx emissions.
• Diagnostic Significance:
  • EGR System Monitoring: Indicates the ECU’s demand for EGR operation.
  • EGR Valve Issues (Combined with EGR Error): Used in conjunction with EGR Error (see below) to diagnose EGR valve malfunctions.

EGR Error

EGR Error is a obd2 live data value representing the percentage difference between the commanded EGR opening and the actual opening of the EGR valve.

• Normal Range: Ideally close to 0%.
• Special Note: If commanded EGR is 0%, EGR error will read:
  • 0% if actual EGR is also 0%.
  • 99.2% if actual EGR is anything other than 0% (indicating “undefined” or not applicable).
• Diagnostic Significance:
  • EGR Valve Malfunction: Significant EGR error values indicate a discrepancy between the commanded and actual EGR valve position, suggesting EGR valve sticking, actuator problems, or sensor issues.
  • EGR System Performance Issues: Persistent EGR errors can lead to increased NOx emissions and potential engine performance problems.

Commanded Diesel Intake Air Flow Control

Commanded Diesel Intake Air Flow Control, also known as EGR Throttle, is a obd2 live data value relevant to some newer diesel engines. It displays data related to a throttle plate used to generate intake vacuum for EGR purposes, including:

• Commanded position of intake air flow throttle plate (0-100% open).

• Actual position of the EGR throttle.

• Commanded position of a second EGR throttle (if fitted).

• Actual position of secondary EGR throttle.

• Normal Range: Throttle plate position varies depending on EGR demand and engine operating conditions.

• Diagnostic Significance:

  • EGR Throttle Issues: Discrepancies between commanded and actual throttle positions indicate EGR throttle malfunctions.
  • EGR System Diagnostics: Provides additional data for diagnosing EGR system problems in diesel engines.

Exhaust Gas Recirculation Temperature

Exhaust Gas Recirculation Temperature is a obd2 live data value reporting up to four EGR temperature values:

• EGRTA – Bank 1 Pre-Cooler.

• EGRTB – Bank 1 Post-Cooler.

• EGRTC – Bank 2 Pre-Cooler.

• EGRTD – Bank 2 Post-Cooler.

• Normal Range: EGR temperature varies depending on EGR system design and operating conditions. EGR coolers are used to reduce EGR gas temperature before re-entering the intake manifold.

• Diagnostic Significance:

  • EGR Cooler Efficiency: Temperature differences between pre-cooler and post-cooler readings can indicate EGR cooler efficiency.
  • EGR System Overheating: Excessively high EGR temperatures can indicate EGR system problems or potential overheating issues.

EVAP System Vapor Pressure

EVAP System Vapor Pressure is a obd2 live data value representing the gauge pressure of the Evaporative Emission Control (EVAP) system, measured from a sensor in the fuel tank or EVAP system line.

• Normal Range: EVAP system pressure typically operates within a slight vacuum or slight positive pressure depending on system operation.
• Diagnostic Significance:
  • EVAP System Leaks: Abnormal pressure readings, especially pressure that does not hold vacuum or positive pressure, are strong indicators of EVAP system leaks (e.g., fuel cap leak, hose leaks, purge valve leaks).
  • EVAP System Blockages: Excessively high vacuum or pressure can indicate blockages in the EVAP system.
  • EVAP Sensor Malfunctions: Incorrect or erratic pressure readings can point to a faulty EVAP pressure sensor.

Absolute Evap System Vapor Pressure

Absolute Evap System Vapor Pressure is a obd2 live data value representing the absolute pressure of the EVAP system, measured from a sensor in the fuel tank or EVAP line. Approximately 14.7 psi or 101.3 kPa indicates 0 gauge pressure.

• Normal Range: Absolute pressure value of EVAP system pressure.
• Diagnostic Significance: Similar to EVAP System Vapor Pressure (Gauge), providing EVAP system pressure readings in absolute terms.

Commanded Evaporative Purge

Commanded Evaporative Purge is a obd2 live data value representing the EVAP purge flow rate requested by the engine computer. 0% is fully closed, 100% is maximum purge flow.

• Normal Range: EVAP purge valve opening varies depending on engine operating conditions and EVAP system strategy. Purge is typically active during part-load cruising conditions.
• Diagnostic Significance:
  • EVAP Purge Valve Monitoring: Indicates the ECU’s demand for EVAP purge operation.
  • EVAP Purge Valve Issues (Combined with other EVAP data): Used in conjunction with other EVAP system data to diagnose purge valve malfunctions.

Catalyst Temperature

Catalyst Temperature is a obd2 live data value representing the temperature of the catalytic converter. “Bank #” indicates the engine bank (bank 1 is typically the side with cylinder #1). “Sensor #” indicates sensor location: #1 is pre-cat, #2 is post-cat.

• Normal Range: Catalyst temperature varies depending on engine load and catalytic converter activity. During normal operation, catalyst temperatures can be quite high (hundreds of degrees Celsius).
• Diagnostic Significance:
  • Catalytic Converter Overheating: Excessively high catalyst temperatures can indicate catalytic converter overheating, which can be caused by rich running conditions, misfires, or catalytic converter malfunctions.
  • Catalytic Converter Efficiency Monitoring: Pre- and post-cat temperature readings can be used to assess catalytic converter efficiency. The post-cat sensor should typically show a lower temperature variation than the pre-cat sensor in a properly functioning converter.
  • Catalytic Converter Failure (Potentially): Extreme temperature deviations or unusual temperature patterns can indicate catalytic converter failure.

Diesel Aftertreatment Status

Diesel Aftertreatment Status is a composite obd2 live data value providing information about the Diesel Particulate Filter (DPF) and NOx adsorber systems on diesel vehicles. It may display:

• Current DPF Regeneration Status: Active/Not Active.

• Current DPF Regeneration Type: Passive/Active.

• NOx Absorber Regen Status: Active/Not Active.

• NOx Absorber Desulfurization Status: Active/Not Active.

• Normalized Trigger for DPF Regen: Percentage until next regen (0% = regen completed, 100% = regen about to start).

• Average Time Between DPF Regens.

• Average Distance Between DPF Regens.

• Normal Range: Status values reflecting different stages of DPF and NOx adsorber operation.

• Diagnostic Significance:

  • DPF Regeneration Monitoring: Provides detailed information about DPF regeneration cycles, including status, type, and frequency.
  • DPF Clogging Indication: Normalized Trigger for DPF Regen value approaching 100% indicates the DPF is becoming full and regeneration is needed.
  • NOx Adsorber System Monitoring: Provides status information for NOx adsorber regeneration and desulfurization processes.
  • Diesel Emissions System Diagnostics: Crucial for diagnosing diesel emissions system problems related to DPF and NOx control.

Diesel Exhaust Fluid Sensor Data

Diesel Exhaust Fluid Sensor Data is a obd2 live data value providing information about the Diesel Exhaust Fluid (DEF) system, including:

• DEF Type: Urea too high, Urea too low, Straight diesel, Proper DEF, Sensor fault.

• DEF Concentration: Urea concentration (should be ~32.5% for proper DEF).

• DEF Tank Temperature.

• DEF Tank Level: Note: Tank level readings may not be progressive; see NOx Control System section for more details.

• Normal Range: Values reflecting proper DEF fluid quality, concentration, temperature, and level.

• Diagnostic Significance:

  • DEF Quality Issues: DEF Type and DEF Concentration readings help diagnose issues with DEF fluid quality or contamination.
  • DEF Tank Level Monitoring: Provides DEF tank level information, although level reporting may be stepped or non-linear on some vehicles.
  • DEF System Malfunctions: Sensor fault readings indicate problems with DEF sensors.
  • SCR System Diagnostics: Crucial for diagnosing Selective Catalytic Reduction (SCR) system problems related to DEF supply and quality.

Diesel Particulate Filter (DPF)

Diesel Particulate Filter (DPF) is a obd2 live data value reporting up to three data points:

• Inlet pressure.
• Outlet pressure.
• Differential pressure across the particulate filter.

Bank 1 vs. Bank 2 indicates the engine bank. Increased differential pressure indicates soot accumulation in the filter.

• Normal Range: DPF pressures vary depending on DPF design and soot loading. Differential pressure should be relatively low in a clean DPF and increase as soot accumulates.
• Diagnostic Significance:
  • DPF Clogging Indication: High DPF differential pressure is a primary indicator of DPF clogging and the need for regeneration.
  • DPF Backpressure Issues: Excessively high DPF inlet pressure can indicate exhaust restrictions upstream of the DPF.
  • DPF Sensor Malfunctions: Incorrect pressure readings can point to faulty DPF pressure sensors.

Diesel Particulate Filter (DPF) Temperature

Diesel Particulate Filter (DPF) Temperature is a obd2 live data value reporting up to two data points for each exhaust bank:

• Inlet temperature.
• Outlet temperature.

Bank 1 vs. Bank 2 indicates the engine bank.

• Normal Range: DPF temperatures vary depending on engine load and DPF regeneration status. DPF temperatures increase significantly during regeneration cycles.
• Diagnostic Significance:
  • DPF Regeneration Monitoring: DPF temperature spikes are expected during regeneration.
  • DPF Overheating (Potentially): Excessively high DPF temperatures can indicate DPF overheating, which can damage the DPF.
  • DPF System Diagnostics: Temperature readings provide valuable data for diagnosing DPF system performance and regeneration issues.

NOx Sensor

NOx Sensor is a hybrid obd2 live data value reporting NOx concentration levels in ppm for up to four sensors:

• Bank 1 Sensor 1.
• Bank 1 Sensor 2.
• Bank 2 Sensor 1.
• Bank 2 Sensor 2.

Bank # indicates engine bank. Sensor number indicates sensor location: #1 is pre-NOx adsorber, #2 is post-NOx adsorber.

• Normal Range: NOx concentration levels should be low downstream of NOx reduction systems in properly functioning diesel engines.
• Diagnostic Significance:
  • NOx Reduction System Efficiency: Pre- and post-NOx adsorber sensor readings are crucial for assessing NOx reduction system efficiency. High post-sensor NOx readings indicate system inefficiency.
  • NOx Sensor Malfunctions: Incorrect or erratic NOx readings can point to faulty NOx sensors.
  • Diesel Emissions Diagnostics: Essential for diagnosing diesel emissions problems related to NOx control.

NOx Control System

NOx Control System is a hybrid obd2 live data value reporting data on the NOx adsorption system, including:

• Average Reagent Consumption Rate: Calculated over the previous 48 hours of engine run time or last 15L consumed.

• Average Demanded Consumption Rate: As commanded by the ECM, calculated similarly.

• Reagent Tank Level: 0-100%. Note: Tank level may not be progressive; see description for details on stepped reporting.

• NOx Warning Indicator Time: Total engine run time in seconds since NOx/SCR warning light activation.

• Normal Range: Reagent consumption rates and tank level should be within expected ranges for proper NOx control system operation.

• Diagnostic Significance:

  • SCR System Monitoring: Provides detailed data for monitoring Selective Catalytic Reduction (SCR) system performance and reagent (DEF) consumption.
  • Reagent Dosing Issues: Discrepancies between demanded and actual reagent consumption rates can indicate reagent dosing problems.
  • DEF Tank Level Monitoring: Provides DEF tank level information and alerts for low DEF levels.
  • NOx Warning System Diagnostics: NOx Warning Indicator Time tracks the duration of NOx warning light activation, indicating potential NOx control system issues.

NOx Sensor Corrected Data

NOx Sensor Corrected Data is a obd2 live data value representing NOx concentration in PPM, including learned adjustments and offsets applied by the system for improved accuracy.

• Normal Range: Similar to NOx Sensor readings but with potential corrections applied.
• Diagnostic Significance: Provides NOx concentration data with potential sensor calibration and correction factors applied for improved accuracy.

NOx NTE Control Area Status

NOx NTE Control Area Status is a obd2 live data value reporting on the NOx “Not-to-Exceed” (NTE) control area, which is a range of engine operation where emissions are tested against NOx limits. It displays:

• Vehicle operating inside/outside NOx control area.

• Vehicle operating inside manufacturer exception/”carve-out” region.

• Vehicle experiencing NTE-related deficiency within NOx control area.

• Normal Range: Status values indicating NTE control area operation.

• Diagnostic Significance:

  • Emissions Compliance Monitoring: Provides data related to NOx emissions compliance within the NTE test region.
  • NTE Deficiency Indication: Indicates if the vehicle is experiencing NOx emissions issues within the NTE control area.
  • Advanced Emissions Diagnostics: Relevant for advanced emissions diagnostics and regulatory compliance.

PM Sensor Bank 1 & 2

PM Sensor Bank 1 & 2 is a obd2 live data value reporting data for Particulate Matter (PM) sensors on banks 1 & 2, including:

• Particulate matter sensor active: yes/no.

• Particulate matter sensor regenerating: yes/no.

• Particulate matter sensor value: 0% (clean) to 100% (regen required).

• Normal Range: Status values reflecting PM sensor activity and regeneration status. PM sensor value should ideally be low (closer to 0%).

• Diagnostic Significance:

  • Particulate Filter Monitoring: Provides data related to particulate filter loading and regeneration status.
  • PM Sensor Performance: Indicates PM sensor activity and readings.
  • Diesel Emissions Diagnostics: Relevant for diagnosing diesel emissions problems related to particulate matter control.

Particulate Matter (PM) Sensor

Particulate Matter (PM) Sensor is a obd2 live data value representing soot concentration as measured by PM sensors on banks 1 & 2, displayed in mg/m3.

• Normal Range: PM concentration should ideally be low in properly functioning diesel emissions systems.
• Diagnostic Significance:
  • Soot Loading Indication: Direct measure of soot concentration in the exhaust.
  • Particulate Filter Performance Assessment: Provides data for assessing particulate filter efficiency and loading.
  • Diesel Emissions Diagnostics: Essential for diagnosing diesel emissions problems related to particulate matter control.

PM NTE Control Area Status

PM NTE Control Area Status is a obd2 live data value reporting on the PM “Not-to-Exceed” (NTE) control area for particulate matter emissions, similar to NOx NTE. It displays:

• Vehicle operating inside/outside PM control area.

• Vehicle operating inside manufacturer exception/”carve-out” region.

• Vehicle experiencing NTE-related deficiency within PM control area.

• Normal Range: Status values indicating PM NTE control area operation.

• Diagnostic Significance:

  • Emissions Compliance Monitoring (PM): Provides data related to particulate matter emissions compliance within the NTE test region.
  • NTE Deficiency Indication (PM): Indicates if the vehicle is experiencing particulate matter emissions issues within the NTE control area.
  • Advanced Emissions Diagnostics (PM): Relevant for advanced emissions diagnostics and regulatory compliance related to particulate matter.

SCR Inducement System

SCR Inducement System is a obd2 live data value reporting on the Selective Catalytic Reduction (SCR) inducement system, which is used to alert drivers to SCR system issues. Inducement strategies may include dash lights, cluster messages, or functional restrictions (torque reduction, limp mode, speed limiter). Inducement triggers include:

• Low reagent level.
• Incorrect reagent used.
• Abnormal reagent consumption rates.
• Excessive NOx emissions.

This parameter reports current SCR inducement status (on/off) and reasons for activation. It also shows if any triggers occurred during the last:

• 0 – 10,000 km.
• 10,000 – 20,000 km.
• 20,000 – 30,000 km.
• 30,000 – 40,000 km.

It may also report total distance traveled during each 10,000 km block with inducement active.

• Normal Range: Inducement status should ideally be “off” during normal operation.
• Diagnostic Significance:
  • SCR System Fault Indication: Indicates when the SCR inducement system is active, signaling a problem with the SCR system.
  • Inducement Trigger Identification: Reports the reasons for inducement activation, helping pinpoint the source of the SCR system issue.
  • SCR System History: Provides historical data on inducement events over different mileage intervals.

NOx Warning And Inducement System

NOx Warning And Inducement System is a obd2 live data value providing information on warning/inducement levels for NOx control systems. Warning/inducement levels are broken down into three levels:

• Level 1: Low severity (e.g., minor power/torque reduction).
• Level 2: Medium severity (e.g., significant power/torque reduction – limp mode).
• Level 3: Severe (e.g., complete engine shutdown, extreme operational limits).

Each level reports one of four statuses:

• Inactive.
• Enabled, but not active (triggered – but not taking effect yet).
• Active.
• Not supported by vehicle.

This parameter also reports (if supported):

• Total engine hours using incorrect reagent.

• Total engine hours with incorrect reagent consumption rate.

• Total engine hours during which reagent dosing was interrupted.

• Total engine hours with DTC for incorrect EGR operation.

• Total engine hours with DTC for incorrect NOx control equipment operation.

• Normal Range: Warning/inducement levels should ideally be “Inactive” during normal operation.

• Diagnostic Significance:

  • NOx Warning System Status: Provides detailed status information about the NOx warning and inducement system, including severity levels and activation status.
  • NOx System Fault History: Tracks engine run time with various NOx system faults, providing historical data on NOx control system issues.
  • Advanced NOx System Diagnostics: Essential for advanced diagnostics of NOx control systems and inducement strategies.

Engine Run Time for AECD

Engine Run Time for AECD is a obd2 live data value related to “Emissions Increasing Auxiliary Emissions Control Devices” (AECD). AECDs are permitted systems that can temporarily disable certain emissions control components under specific conditions. This parameter displays the total time (in seconds) each AECD was active. It does not provide details about AECD purpose or operation; a factory manual may be needed for AECD-specific information. Each listed AECD may display one or two timers:

• One Timer Used:
  • TIME1: Total engine run time with AECD active.
  • TIME2: Maximum value (136 years) to indicate ‘not used’.
• Two Timers Used:
  • TIME1: Engine run time with AECD inhibiting up to 75% of emissions control performance.
  • TIME2: Engine run time with AECD inhibiting emissions control beyond 75%.

These timers cannot be reset by a scan tool or battery disconnection.

• Normal Range: AECD run time should ideally be minimal during normal operation, as AECDs are intended for specific, limited conditions.
• Diagnostic Significance:
  • AECD Activity Monitoring: Tracks the operational time of AECDs, providing data on how often these devices are active.
  • Emissions System Analysis: AECD run time data can be relevant for in-depth emissions system analysis and understanding the vehicle’s emissions control strategy.
  • Advanced Diagnostics: Provides data for advanced diagnostics related to emissions control system operation and AECD usage.

By understanding these obd2 live data values and their diagnostic significance, automotive professionals and enthusiasts can leverage the power of OBD2 diagnostics to effectively troubleshoot vehicle issues, ensure optimal performance, and maintain vehicle health. This comprehensive guide provides a solid foundation for interpreting live data and utilizing it for efficient and accurate automotive repairs.