Throttle/Pedal Position Sensor/Switch "D" Circuit Low
The engine control module detected an abnormally low voltage signal from the Throttle Position Sensor (TPS) D circuit, indicating either a circuit short to ground, poor sensor connection, or faulty sensor. This prevents the PCM from accurately reading throttle input, disrupting fuel and ignition timing control.
What You Might Notice
- Rough or unstable idle
- Engine stalling at stops or while driving
- Engine surging or hesitation
- Reduced or no acceleration response
- Check Engine light illumination
Most Common Causes
- 1
Faulty Throttle Position Sensor
The TPS itself is failing or out of calibration, sending an abnormally low voltage signal to the PCM. This is the most common cause of P2122.
- 2
TPS Circuit Short to Ground
The wiring harness or connector for the TPS has a short circuit that is pulling the signal voltage down toward ground. This can occur due to damaged insulation or corroded connectors.
- 3
Loose or Improperly Mounted TPS
The sensor is not secured correctly to the throttle body, causing intermittent poor electrical contact or misalignment that affects the signal output.
- 4
Faulty Engine Control Module (PCM)
Rarely, the PCM itself may be defective and incorrectly interpreting a normal TPS signal as low voltage, though this is uncommon compared to sensor or wiring faults.
How to Diagnose It
- 1
Check Faulty Throttle Position Sensor — The TPS itself is failing or out of calibration, sending an abnormally low voltage signal to the PCM. This is the most common cause of P2122.
- 2
Check TPS Circuit Short to Ground — The wiring harness or connector for the TPS has a short circuit that is pulling the signal voltage down toward ground. This can occur due to damaged insulation or corroded connectors.
- 3
Check Loose or Improperly Mounted TPS — The sensor is not secured correctly to the throttle body, causing intermittent poor electrical contact or misalignment that affects the signal output.
- 4
Check Faulty Engine Control Module (PCM) — Rarely, the PCM itself may be defective and incorrectly interpreting a normal TPS signal as low voltage, though this is uncommon compared to sensor or wiring faults.
How to Fix It
- 1
Inspect and Reseat TPS Connector
Locate the TPS connector and disconnect it, inspect for corrosion or damage, clean the contacts with electrical contact cleaner, and reconnect firmly. Verify the connector seats completely and locks in place.
- 2
Replace Throttle Position Sensor
If the connector is secure and clean, the TPS is likely faulty. Remove the old sensor from the throttle body and install a new OEM or quality replacement sensor, ensuring it is properly calibrated per manufacturer specifications.
- 3
Inspect TPS Wiring and Circuit
Visually trace the TPS wiring harness from the sensor to the PCM, looking for cuts, pinches, or corrosion. Use a multimeter to check for continuity and shorts to ground. Repair or replace damaged wiring sections.
- 4
Verify PCM Function and Clear Code
After repairs, use a diagnostic scanner to confirm the circuit voltage is within normal range (typically 0.5–4.5V), clear the DTC, and perform a test drive to ensure the code does not return. If the code persists after sensor and wiring repairs, PCM replacement may be necessary.
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