Understanding the language of automotive diagnostics can often feel like deciphering a complex code. With the advent of On-Board Diagnostics II (OBD2), a standardized system was introduced to help mechanics and car owners alike understand vehicle health and troubleshoot issues. Within this vast terminology, “Fli Obd2,” referring to the Fuel Level Indicator within the OBD2 system, plays a crucial role in diagnosing fuel-related problems. This guide serves as your comprehensive dictionary to navigate the world of OBD2 terms, ensuring you’re well-equipped to understand your vehicle’s diagnostic outputs.
OBD2 Terms: Acronyms and Definitions Explained
Navigating car diagnostics often involves encountering a plethora of acronyms and technical terms. This section breaks down common OBD2 terms into easily digestible definitions, helping you understand what these abbreviations mean in the context of vehicle repair and maintenance.
List 1: Essential OBD2 Acronyms
| Term | Definition |
|---|---|
| AFC | Air Flow Control – System that manages the amount of air entering the engine, crucial for optimal combustion and emissions. |
| ALDL | Assembly Line Diagnostic Link. An older term, primarily for General Motors, referring to the diagnostic connector socket used before OBD2 standardization. Sometimes used broadly for pre-OBD II computer signals. |
| CAN | Controller Area Network – A robust communication protocol that allows different electronic control units (ECUs) within a vehicle to communicate with each other without a central host computer. |
| CARB | California Air Resources Board – The clean air agency in the government of California. It is responsible for researching the adverse health effects of pollution and for setting and enforcing emission standards for vehicles. |
| CFI | Central Fuel Injection (a.k.a. Throttle Body Fuel Injection TBI) – A fuel injection system where fuel is injected at a central point above the throttle body, rather than directly into the cylinders. |
| CFI | Continuous Fuel Injection – A type of fuel injection system that continuously injects fuel into the intake manifold, as opposed to injecting fuel intermittently. |
| CO | Carbon Monoxide – A colorless, odorless, and toxic gas produced by incomplete combustion of fuel. Monitored by OBD2 systems as part of emissions control. |
| DLC | Data Link Connector – The standardized 16-pin connector in your vehicle where scan tools are plugged in to access OBD2 data. |
| Driving Cycle | A specific, standardized sequence of driving conditions (including start-up, warm-up, and various driving maneuvers) designed to allow all OBD2 monitors to run their diagnostic tests. |
| DTC | Diagnostic Trouble Code – A code stored by the vehicle’s computer when a fault is detected in a system. DTCs help identify the source of problems. |
| ECM | Engine Control Module – The main computer in the vehicle that controls engine operation and emissions systems. Often interchangeable with ECU and PCM. |
| ECT | Engine Coolant Temperature – Sensor that measures the temperature of the engine coolant. Critical for engine management and temperature monitoring. |
| ECU | Engine Control Unit – Similar to ECM, often used interchangeably to refer to the computer controlling the engine. |
| EEC | Electronic Engine Control – A general term for systems that electronically manage engine functions. |
| EEPROM or E2PROM | Electrically Erasable Programmable Read Only Memory – A type of memory chip in the ECU that can be reprogrammed electronically, even after being installed in the vehicle. |
| EFI | Electronic Fuel Injection – A system that uses electronic controls to inject fuel into the engine, offering more precise fuel delivery than older carburetor systems. |
| EGR | Exhaust Gas Recirculation – A system that recirculates a portion of the engine’s exhaust gas back into the intake manifold to reduce NOx emissions. |
| EMR | Electronic Module Retard – Refers to electronically controlled ignition timing retard, often used for knock control. |
| EPA | Environmental Protection Agency. The US federal agency responsible for protecting human health and the environment. Its Office of Mobile Sources deals with vehicle emissions regulations. |
| ESC | Electronic Spark Control – An early form of electronic ignition timing control. |
| EST | Electronic Spark Timing – Electronically controlled system for adjusting ignition timing for optimal engine performance and emissions. |
| DPFE | Differential Pressure Feedback EGR sensor – A specific type of EGR sensor used in Ford OBD2 systems to measure the pressure difference across the EGR valve, monitoring EGR flow. |
| DTC | Diagnostic Trouble Code – (Redundant entry, see above) |
| FLI | Fuel Level Indicator – Indicates the amount of fuel in the vehicle’s fuel tank. In OBD2 context, this data is often monitored and accessible through scan tools, providing insights into fuel system operation. |
| Fuel Trim | An adaptive engine control function that adjusts the air/fuel mixture to maintain the ideal stoichiometric ratio (14.7:1 air to fuel) for optimal catalytic converter efficiency and emissions. |
| HC | Hydrocarbons – Unburned fuel emissions. Monitored by OBD2 as part of emissions control. |
| HEI | High Energy Ignition – A type of electronic ignition system that provides a higher voltage spark for improved combustion. |
| HO2S | Heated Oxygen Sensor – An oxygen sensor with a built-in heater to bring it up to operating temperature quickly for faster closed-loop operation and reduced emissions. |
| IAT | Intake Air Temperature – Sensor that measures the temperature of the air entering the engine’s intake manifold. Used for air density calculations and engine management. |
| ISO 9141 | International Standards Organization OBDII communication mode – One of the OBD2 communication protocols, commonly used by Chrysler and many foreign car manufacturers. |
| J1850PWM | (Pulse Width Modulated) SAE-established OBD II communication standard – An OBD2 communication protocol used by Ford domestic vehicles and light trucks. |
| J1850VPW | (Variable Pulse Width Modulated) SAE-established OBD II communication standard – An OBD2 communication protocol used by GM vehicles and light trucks. |
| J1962 | SAE-established standard for the connector plug layout – Defines the physical characteristics and pin assignments of the OBD2 Data Link Connector (DLC). |
| J1978 | SAE-established standard for OBD II scan tools – Defines the minimum functional requirements and performance criteria for OBD2 scan tools. |
| J1979 | SAE-established standard for diagnostic test modes – Specifies the standardized diagnostic test modes and services that all OBD2 compliant vehicles must support. |
| J2012 | SAE-established standard accepted by EPA as the standard test report language for emission tests – Defines standardized Diagnostic Trouble Codes (DTCs) for emissions-related faults, ensuring consistency across manufacturers. |
| MAF | Mass Air Flow – Sensor that measures the mass of air flowing into the engine. Crucial for accurate air/fuel ratio control. |
| MAP | Manifold Absolute Pressure – Sensor that measures the absolute pressure in the intake manifold. Used for air density and load calculations. |
| MAT | Manifold Air Temperature – (Redundant, see IAT – Intake Air Temperature, often used interchangeably) |
| MFG | Manufacturer – Abbreviation for vehicle manufacturer. |
| MIL | Malfunction Indicator Light. Commonly known as the “Check Engine Light” on the dashboard. Illuminates when the OBD2 system detects an emissions-related fault. |
| NOx | Oxides of Nitrogen – A group of harmful emissions formed at high combustion temperatures. Controlled by EGR and catalytic converters. |
| O2 | Oxygen – Monitored in the exhaust stream by oxygen sensors to ensure proper combustion and catalytic converter operation. |
| OBD | On-Board Diagnostics – A vehicle’s self-diagnostic and reporting capability. OBD2 is the second generation of this standard. |
| OBDII or OBD 2 | Updated On-Board Diagnostics standard – The standardized OBD system mandated in the US for all cars and light trucks manufactured after January 1, 1996. Provides comprehensive emissions monitoring and diagnostic capabilities. |
| Parameters | Data readings from sensors and calculated values reported by the OBD2 system. Accessible through scan tools and represent various engine and system functions. |
| PCM | Powertrain Control Module – A computer that controls both the engine and the transmission. In many modern vehicles, the PCM integrates the functions of the ECM and TCM. |
| PCV | Positive Crankcase Ventilation – A system that vents crankcase gases back into the intake manifold to be burned, reducing emissions and preventing pressure buildup in the crankcase. |
| PID | Parameter ID – A code used to request specific data parameters from the OBD2 system. |
| Proprietary Readings | Diagnostic data parameters that are not part of the standardized OBD2 requirements but are added by vehicle manufacturers for more in-depth diagnostics of specific vehicle systems. |
| PTC | Pending Trouble Code – A DTC that is stored temporarily after a fault is detected but has not yet been confirmed during subsequent driving cycles. |
| RPM | Revolutions Per Minute – Measures engine speed. A fundamental parameter in engine diagnostics. |
| SAE | Society of Automotive Engineers – A professional organization that develops standards for various aspects of engineering, including the OBD2 standards adopted by the EPA. |
| Scan Tool | An electronic device used to interface with a vehicle’s OBD2 system, read DTCs, display sensor data, and perform diagnostic tests. |
| SES | Service Engine Soon dash light – An older term for the Malfunction Indicator Light (MIL). |
| SFI | Sequential Fuel Injection – A type of fuel injection system where fuel is injected individually and sequentially into each cylinder’s intake port, timed with the engine’s firing order for optimal performance. |
| Stoichiometric Ratio | Theoretical perfect combustion ratio of 1 part gasoline to 14.7 parts air – The ideal air/fuel mixture for complete combustion and efficient catalytic converter operation. |
| TBI | Throttle Body Injection – (See CFI – Central Fuel Injection, often used interchangeably) |
| TPI | Tuned Port Injection – A type of multi-port fuel injection system designed to optimize intake airflow and improve engine performance. |
| TPS | Throttle Position Sensor – Sensor that measures the position of the throttle plate, indicating driver demand and engine load. |
| VAC | Vacuum – Manifold vacuum is a measure of engine load and condition. Used in various engine control systems. |
| VCM | Vehicle Control Module – A more comprehensive computer module that can oversee engine management, transmission control, ABS, and other vehicle systems, extending beyond just emissions control. |
| VIN | Vehicle Identification Number – A unique serial number assigned to each vehicle. Used for vehicle identification and tracking. |
| VSS | Vehicle Speed Sensor – Sensor that measures the speed of the vehicle. Used by various systems including the speedometer, cruise control, and transmission control. |
| WOT | Wide Open Throttle – The condition when the accelerator pedal is fully pressed, and the throttle plate is fully open, demanding maximum engine power. |
List 2: Expanded List of Automotive Acronyms
This list provides a broader range of automotive acronyms, including many that are related to OBD2 and vehicle systems in general.
| Term | Definition |
|---|---|
| A/C | Air Conditioning |
| AC | Air Cleaner |
| AIR | Secondary Air Injection |
| A/T | Automatic Transmission or Transaxle |
| B+ | Battery Positive Voltage |
| BARO | Barometric Pressure |
| BCM | Body Control Module |
| CAC | Charge Air Cooler |
| CFI | Continuous Fuel Injection |
| CL | Closed Loop |
| CKP | Crankshaft Position Sensor |
| CKP REF | Crankshaft Reference |
| CMP | Camshaft Position Sensor |
| CMP REF | Camshaft Reference |
| CO | Carbon Monoxide |
| CO2 | Carbon Dioxide |
| CPP | Clutch Pedal Position |
| CTOX | Continuous Trap Oxidizer |
| CTP | Closed Throttle Position |
| DEPS | Digital Engine Position Sensor |
| DFCO | Decel Fuel Cut-Off Mode |
| DFI | Direct Fuel Injection |
| DIC | Driver Information Center |
| DLC | Data Link Connector |
| DTC | Diagnostic Trouble Code |
| DTM | Diagnostic Test Mode |
| EBCM | Electronic Brake Control Module |
| EBTCM | Electronic Brake Traction Control Module |
| EC | Engine Control |
| ECM | Engine Control Module |
| ECL | Engine Coolant Level |
| ECT | Engine Coolant Temperature |
| EEPROM | Electrically Erasable Programmable Read Only Memory |
| EFE | Early Fuel Evaporation |
| EGR | Exhaust Gas Recirculation |
| EGRT | EGR Temperature |
| EI | Electronic Ignition |
| EPROM | Erasable Programmable Read Only Memory |
| EVAP | Evaporative Emission System |
| FC | Fan Control |
| FF | Flexible Fuel |
| FP | Fuel Pump |
| FT | Fuel Trim |
| FTP | Federal Test Procedure |
| GCM | Governor Control Module |
| GEN | Generator (Alternator) |
| GND | Ground |
| H20 | Water |
| HO2S | Heated Oxygen Sensor |
| HO2S1 | Upstream Heated Oxygen Sensor |
| HO2S2 | Up or Downstream Heated Oxygen Sensor |
| HO2S3 | Downstream Heated Oxygen Sensor |
| HC | Hydrocarbon |
| HVAC | Heating Ventilation and Air Conditioning System |
| IA | Intake Air |
| IAC | Idle Air Control |
| IAT | Intake Air Temperature |
| IC | Ignition Control Circuit |
| ICM | Ignition Control Module |
| IFS | Inertia Fuel Shutoff |
| I/M | Inspection/Maintenance |
| I/M 240 | Inspection/Maintenance 240 Emissions Test |
| IPC | Instrument Panel Cluster |
| ISC | Idle Speed Control |
| KOEC | Key On, Engine Cranking |
| KOEO | Key On, Engine Off |
| KOER | Key On, Engine Running |
| KS | Knock Sensor |
| KSM | Knock Sensor Module |
| LEV | Low Emission Vehicle |
| LT | Long Term Fuel Trim |
| MAF | Mass Airflow Sensor |
| MAP | Manifold Absolute Pressure Sensor |
| MC | Mixture Control |
| MDP | Manifold Differential Pressure |
| MFI | Multiport Fuel Injection |
| MIL | Malfunction Indicator Lamp |
| MPH | Miles Per Hour |
| NOX | Oxides of Nitrogen |
| O2S | Oxygen Sensor |
| OBD | Onboard Diagnostics |
| OBD I | Onboard Diagnostics Generation One |
| OBD II | Onboard Diagnostics, Second Generation |
| OC | Oxidation Catalyst |
| ODM | Output Device Monitor |
| OL | Open Loop |
| OSC | Oxygen Sensor Storage |
| PAIR | Pulsed Secondary Air Injection |
| PCM | Powertrain Control Module |
| PCV | Positive Crankcase Ventilation |
| PNP | Park/Neutral Switch |
| PROM | Program Read Only Memory |
| PSA | Pressure Switch Assembly |
| PSP | Power Steering Pressure |
| RAM | Random Access Memory |
| RM | Relay Module |
| ROM | Read Only Memory |
| RPM | Revolutions Per Minute (Engine Speed) |
| SC | Supercharger |
| SCB | Supercharger Bypass (Wastegate) |
| SDM | Sensing Diagnostic Mode |
| SFI | Sequential Fuel Injection |
| SRI | Service Reminder Indicator |
| SRT | System Readiness Test |
| ST | Short Term Fuel Trim |
| TB | Throttle Body |
| TBI | Throttle Body Injection |
| TC | Turbocharger |
| TCC | Torque Converter Clutch |
| TCM | Transmission or Transaxle Control Module |
| TFP | Throttle Fluid Pressure |
| TP | Throttle Position |
| TPS | Throttle Position Sensor |
| TVV | Thermal Vacuum Valve |
| TWC | Three Way Catalyst |
| TWC+OC | Three Way + Oxidation Catalytic Converter |
| ULEV | Ultra Low Emission Vehicle |
| VAF | Volume Airflow |
| VCM | Vehicle Control Module |
| VR | Voltage Regulator |
| VS | Vehicle Sensor |
| VSS | Vehicle Speed Sensor |
| WU-TWC | Warm Up Three Way Catalytic Converter |
| WOT | Wide Open Throttle |
| ZEV | Zero Emission Vehicle |
Technical Terms in Automotive Diagnostics
Beyond acronyms, understanding the technical terms used in automotive diagnostics is equally important. This section defines key concepts that are fundamental to comprehending OBD2 diagnostics and vehicle repair.
Essential Diagnostic Terminology
| Term | Definition |
|---|---|
| Baud Rate | The speed at which data bits are transmitted in digital communication, especially within a vehicle’s network. It determines how quickly information is exchanged between modules on the CAN bus or through the serial data stream. |
| Bus | In automotive context, “bus” refers to the communication network (like the Controller Area Network – CAN bus) that allows different electronic modules in a vehicle to exchange data. It acts as a pathway for signals and information throughout the vehicle’s electronic systems. |
| CAN (Controller Area Network) | A specialized, robust network standard designed to allow ECUs and other devices within a vehicle to communicate with each other. CAN bus systems are crucial for modern vehicle operation, enabling complex interactions between systems like engine management, braking, and stability control. Communication issues on the CAN bus can lead to various drivability problems and fault codes. |
| Closed Loop | An operational mode in fuel control systems where the Engine Control Module (ECM) actively adjusts the air-fuel mixture based on feedback from the oxygen sensor(s). Closed loop operation is essential for optimal emissions and fuel efficiency. It typically engages once the engine and oxygen sensor are at operating temperature. Factors like faulty coolant sensors, oxygen sensors, or thermostats can prevent closed loop operation, often resulting in a rich-running and polluting engine. |
| Code Reader | A basic diagnostic tool that plugs into the OBD2 Data Link Connector (DLC) and displays Diagnostic Trouble Codes (DTCs). Code readers are useful for retrieving and clearing fault codes and may show OBD2 readiness flags. However, they generally have limited capabilities compared to scan tools and often cannot access sensor data or perform advanced system diagnostics. |
| Downstream O2 sensor | The oxygen sensor positioned after the catalytic converter in the exhaust system. Its primary function is to monitor the efficiency of the catalytic converter by measuring oxygen levels in the post-catalyst exhaust. It can also play a role in long-term fuel trim adjustments in some vehicles. |
| Drive Cycle | A complete sequence of engine operation, typically involving starting the engine, allowing it to reach normal operating temperature, performing specific driving maneuvers (or idling), and then shutting it off. Drive cycles are critical for running OBD2 monitors and confirming repairs after service. |
| Enable Criteria | The specific set of conditions that must be met for an OBD2 diagnostic monitor or test to run. These criteria can include engine temperature, speed, load, and duration of operation. Understanding enable criteria is essential for diagnosing intermittent faults and ensuring all OBD2 monitors have completed. |
| Fuel Trim | The fine-tuning adjustments made to the air-fuel mixture by the engine control system. Fuel trim exists in two forms: short-term and long-term. Short-term fuel trim reacts quickly to changing driving conditions. Long-term fuel trim compensates for gradual changes due to engine wear, sensor drift, or component aging, maintaining optimal air-fuel ratio over time. |
| Loaded Mode Testing | A type of emissions testing that simulates real-world driving conditions by placing a load on the vehicle’s drivetrain. This is typically done using a dynamometer while the vehicle is driven through various speed and load cycles. Loaded mode testing (used in tests like I/M 240 and ASM) provides a more accurate assessment of a vehicle’s emissions performance compared to idle or static testing. |
| Misfire Detection | An OBD2 monitoring function that detects engine misfires – instances where combustion is incomplete or absent in one or more cylinders. Misfires can be caused by issues with ignition, fuel delivery, or compression. If misfire rates exceed certain thresholds, OBD2 will set misfire-related DTCs, often indicating the specific cylinder(s) involved. A “random misfire” code (P0300) suggests a broader issue like vacuum leaks, EGR leaks, or low fuel pressure. |
| Monitor | An OBD2 self-diagnostic test or routine that the vehicle’s computer runs to check the functionality and performance of a specific system or component related to emissions control. OBD2 monitors are designed to detect malfunctions that could increase vehicle emissions. |
| Open Loop | An operational mode of the fuel control system where the air-fuel mixture is predetermined and fixed by the Engine Control Module (ECM), without feedback from the oxygen sensor(s). Open loop typically occurs during engine startup, warm-up, and under heavy load conditions. In open loop, the system does not adjust fuel based on real-time exhaust gas analysis. |
| Readiness Code or Flag | An OBD2 status indicator that shows whether a specific emission-related monitor has run and completed its diagnostic test. Readiness flags are crucial for emissions testing; most jurisdictions require that all but one or two readiness monitors are in a “ready” state (completed) for a vehicle to pass an OBD2 emissions inspection. Specific requirements vary by model year and location. |
| Scan Tool | An advanced diagnostic device that connects to the OBD2 DLC, offering comprehensive access to vehicle system information. Scan tools can read DTCs (including history codes and pending codes), display live sensor data, perform bidirectional tests (activating components to test their function), and in some cases, reprogram vehicle computers. Professional-grade scan tools offer extensive diagnostic and repair capabilities. |
| Trip | Refers to operating a vehicle under conditions and for a duration sufficient to allow all applicable OBD2 monitors to run at least once. Completing a “trip” is often necessary to set readiness flags and confirm that diagnostic tests have been performed after repairs or code clearing. |
| Upstream O2 sensor | The oxygen sensor located in the exhaust manifold, before (upstream of) the catalytic converter. This sensor is the primary sensor used by the fuel control system to measure the air-fuel mixture’s richness or leanness. The upstream O2 sensor’s feedback is crucial for maintaining the stoichiometric air-fuel ratio for optimal emissions, fuel economy, and engine performance. |
| Warm-up Cycle | Starting an engine when it’s cold and allowing it to reach a specified temperature increase and minimum operating temperature. A warm-up cycle is often defined as starting with an engine temperature below a certain threshold (e.g., below 40 degrees F or 22 degrees C), increasing the engine temperature by at least 40 degrees F (22 degrees C), and reaching a minimum temperature of 160 degrees F (70 degrees C). Warm-up cycles are relevant to OBD2 monitor operation and drive cycle completion. |
This glossary aims to demystify the technical jargon associated with OBD2 systems and automotive diagnostics. By understanding these terms, you can better interpret diagnostic information, communicate effectively with automotive professionals, and take informed decisions about your vehicle’s maintenance and repair, especially when dealing with systems related to “FLI OBD2” and fuel management.
