Throttle/Pedal Position Sensor A Circuit Low
The Powertrain Control Module (PCM) detected that the voltage signal from Throttle/Pedal Position Sensor A is lower than the expected minimum threshold. This typically indicates a short to ground, a faulty sensor, or an open circuit in the sensor wiring.
This code is considered high severity because it directly affects the engine's ability to accelerate and can trigger a reduced power 'limp mode'. It should be addressed immediately to ensure safe vehicle operation.
Common symptoms
- Check Engine Light illuminated
- Poor or hesitant acceleration
- Engine stalling or rough idling
- Vehicle stuck in reduced power or 'limp' mode
- Unusually high or erratic idle speed
Likely causes
- Faulty Throttle Position Sensor (TPS) or Pedal Position Sensor
- Damaged, corroded, or loose wiring connector at the sensor
- Short to ground in the sensor signal circuit
- Open circuit in the sensor wiring harness
- Faulty Powertrain Control Module (PCM) (rare)
What to check before replacing parts
Inspect the TPS/PPS wiring and connector.
Look for: Loose pins, corrosion, or frayed wires that could cause an open or short circuit.
Scan for freeze frame data and other related codes.
Look for: Concurrent 5-volt reference codes or other TPS codes that might indicate a shared circuit issue rather than an isolated sensor failure.
Test the 5-volt reference and ground circuits at the sensor connector with a multimeter.
Look for: A steady 5 volts on the reference pin and good continuity to ground; missing voltage indicates a wiring or PCM issue.
Measure the signal voltage from the sensor while slowly sweeping the throttle or pedal.
Look for: A smooth voltage increase from about 0.5V to 4.5V; dropouts or a constant low voltage under 0.2V confirm a bad sensor.
Perform a continuity test on the signal wire between the sensor and the PCM.
Look for: High resistance or infinite resistance (OL) indicating a broken wire in the harness.
This page explains the generic P0122 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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