When your car’s check engine light illuminates and a scan tool reveals the Obd2 Code P0122, it indicates a problem within the Throttle Position Sensor (TPS) circuit. As an essential component in your vehicle’s engine management system, the TPS plays a crucial role in how your car performs. This article will delve into the specifics of the P0122 code, helping you understand its causes, symptoms, and diagnostic procedures.
Understanding the Throttle Position Sensor and Code P0122
The Throttle Position Sensor is essentially a potentiometer mounted on the throttle body. It measures the throttle blade’s angle and sends this information as a voltage signal to the Powertrain Control Module (PCM). The PCM relies heavily on this signal to determine engine load and adjust fuel delivery, ignition timing, and transmission operation accordingly.
Typically, the TPS receives a 5-volt reference signal from the PCM. At idle, the TPS signal voltage should be around 0.6 volts, increasing to over 4.0 volts when the throttle is wide open (WOT). OBD2 code P0122 is triggered when the PCM detects that the TPS signal voltage is abnormally low – specifically, less than 0.2 volts for a sustained period (in this case, 10 seconds). This “low voltage” condition signals a potential fault in the TPS circuit.
Alt text: Location of the Throttle Position Sensor on a car engine throttle body, highlighting its position and connection to the throttle linkage for OBD2 code P0122 troubleshooting.
Symptoms of OBD2 Code P0122
When the P0122 code is active, you may notice several symptoms affecting your vehicle’s performance:
- Check Engine Light: The most immediate sign is the illumination of the Malfunction Indicator Lamp (MIL), commonly known as the check engine light.
- Poor Engine Performance: Expect issues like hesitation, stumbling, or lack of power, especially during acceleration.
- Rough Idle: The engine might idle erratically or stall.
- Transmission Problems: The PCM uses TPS data for transmission control, so you might experience:
- Hard or erratic shifting.
- Transmission Control Converter (TCC) engagement issues.
- High transmission line pressure.
- Fixed shift points or inability to shift into overdrive (like fourth gear in some vehicles).
- Vehicle in Limp Mode: In some cases, the PCM might enter a “limp mode” to protect the engine and transmission, severely restricting vehicle speed and performance.
Potential Causes of OBD2 Code P0122
Several factors can lead to a P0122 code. These can be broadly categorized as:
- Faulty Throttle Position Sensor (TPS): The sensor itself might be malfunctioning, providing an inaccurate low voltage signal.
- Wiring Issues: Problems in the TPS circuit wiring are common culprits:
- Short to Ground: The TPS signal wire might be shorted to ground, causing a low voltage reading.
- Open Circuit: A break in the wiring (open circuit) in the signal, reference, or ground wires can disrupt the signal.
- Poor Connection: Corroded or loose connectors at the TPS or PCM can cause signal degradation.
- Damaged Wiring: Rubbed, frayed, or damaged wiring insulation can lead to shorts or opens.
- PCM Issues: Although less frequent, a fault within the PCM itself, specifically in the 5-volt reference circuit or the TPS signal processing, can trigger P0122.
- 5-Volt Reference Circuit Problem: If the 5-volt reference circuit supplying power to the TPS is shorted to ground or another voltage, it can affect the TPS signal. Note that the 5-volt reference circuit often powers other sensors as well (like the Fuel Tank Pressure Sensor).
Diagnosing and Repairing OBD2 Code P0122
Diagnosing code P0122 requires a systematic approach. Here’s a step-by-step diagnostic procedure based on a typical troubleshooting flow, which may require tools like a scan tool and a multimeter:
Step 1: Initial OBD System Check
Begin with a complete OBD system check using a scan tool. Verify the presence of DTC P0122 and check for any other related codes, particularly P1639 (5 Volt Reference 2 Circuit). If P1639 is present, it suggests a broader issue with the 5-volt reference circuit, possibly a short to ground or voltage. Address P1639 first.
Step 2: Verify Code P0122 and TPS Voltage
With the engine idling, use the scan tool to monitor live data, specifically the TPS voltage. Check if DTC P0122 is currently failing (“fail this ignition”) and if the TPS voltage is indeed below the specified low threshold (0.2V).
Step 3: Review Freeze Frame Data and Replicate Conditions
If the TPS voltage is not initially low, review the Freeze Frame and/or Failure Records data stored by the PCM when the P0122 code was set. Note the conditions (RPM, load, vehicle speed, temperature, etc.). Turn off the ignition for 15 seconds, restart the engine, and attempt to replicate the conditions recorded in the Freeze Frame data. Monitor if the P0122 code reappears.
Step 4: Disconnect Accelerator and Servo Control Module (If Applicable)
In some systems, the Accelerator and Servo Control Module can influence TPS readings. Disconnect this module (refer to your vehicle’s service manual for proper procedure). With the ignition ON and engine OFF, check if the TPS voltage is still below 0.2V. If the voltage reading corrects after disconnection, the issue might lie within the Accelerator and Servo Control Module system.
Alt text: Close-up of a Throttle Position Sensor connector, illustrating the electrical interface for diagnosing OBD2 code P0122 related to wiring or sensor connection issues.
Step 5: Test TPS Circuit with Jumper Wire
Disconnect the electrical connector from the TPS. Using a jumper wire, connect the 5-volt reference circuit wire to the TPS signal circuit wire at the harness connector. With the ignition ON and engine OFF, observe the TPS voltage reading on the scan tool. It should now read high, close to 4.7V (specified value).
- If voltage is high (around 4.7V): This indicates the wiring to the PCM is likely good. Proceed to Step 12 (replace the TPS sensor).
- If voltage is still low: Proceed to Step 7.
Step 6: Test TPS Signal Circuit with Test Lamp
Connect a test lamp between a 12V battery positive (B+) and the TPS signal circuit wire at the TPS harness connector. Observe the TPS voltage on the scan tool. It should now read high (around 4.7V).
- If voltage is high (around 4.7V): This suggests a possible open or high resistance in the TPS signal circuit pulling the voltage down. Proceed to Step 8 to check the 5-volt reference circuit wiring.
- If voltage is still low: Proceed to Step 10 to directly test the TPS signal circuit for shorts or opens.
Step 7: Check 5-Volt Reference Circuit Wiring
Turn OFF the ignition and disconnect the PCM connector (typically C2). Test the 5-volt reference circuit wire for:
- Open circuit: Check for continuity.
- Short to ground: Check for resistance to ground.
Repair any identified wiring issues (shorts or opens).
Step 8: Check 5-Volt Reference Circuit Connection at PCM
If no wiring issues are found in Step 7, inspect the 5-volt reference circuit terminal at the PCM connector for poor connections (corrosion, bent pins, etc.). Repair as needed.
Step 9: Test TPS Signal Circuit Wiring
Turn OFF ignition and disconnect the PCM connector (C2). Test the TPS signal circuit wire for:
- Open circuit: Check for continuity.
- Short to ground: Check for resistance to ground.
- Short to sensor ground circuit: Check for shorts to the sensor ground wire.
Repair any wiring faults.
Step 10: Check TPS Signal Circuit Connection at PCM
Inspect the TPS signal circuit terminal at the PCM connector for poor connections. Repair if necessary.
Step 11: Replace Throttle Position Sensor (TPS)
If the wiring and PCM connections are verified as good, replace the Throttle Position Sensor.
Step 12: Replace Powertrain Control Module (PCM)
If replacing the TPS doesn’t resolve the P0122 code, and all wiring is confirmed to be in good condition, PCM replacement might be necessary. Important: PCM replacement often requires programming to match your vehicle’s specific configuration.
Step 13: Verify Repair and Clear Codes
After any repair, clear DTC P0122 and any other stored codes using a scan tool. Start the engine, allow it to reach normal operating temperature, and perform a system check using the scan tool to confirm that the diagnostic test for P0122 runs and passes.
Step 14: Final System Check
Review the scan tool data for any remaining DTCs. If no other codes are present, the system is OK. If other codes are present, diagnose them accordingly.
Conclusion
OBD2 code P0122 indicates a low voltage issue with your Throttle Position Sensor circuit, which can lead to various driveability problems. By systematically following the diagnostic steps outlined above, you can effectively pinpoint the root cause, whether it’s a faulty sensor, wiring problem, or, less commonly, a PCM issue. Remember to always consult your vehicle’s service manual for specific procedures and wiring diagrams. Addressing code P0122 promptly will restore your vehicle’s performance and ensure optimal engine and transmission operation.
