P057CBrake Pedal Position Sensor "A" Circuit Low
The brake pedal position sensor signal voltage is stuck below its normal operating range.
Definition
The PCM monitors the brake pedal position sensor's analog signal, which should stay within a defined window (typically about 0.5-4.5 V) across full pedal travel. P057C sets when the signal drops below the minimum threshold, indicating a short to ground, an open signal wire on some designs, a failed sensor, or a missing 5 V supply. The module substitutes a failsafe value, which commonly disables cruise control and smart-entry starting, may keep brake lights from working correctly on sensor-driven systems, and reduces regenerative braking on hybrids.
Common causes
- Brake pedal position sensor signal wire shorted to ground
- Failed sensor with a dead output
- Open or shorted 5 V reference supply to the sensor
- Chafed harness near the pedal assembly grounding the signal
- Corroded or water-contaminated connector
- Faulty control module (rare)
Common misdiagnoses
- Replacing the brake light switch
- Replacing the sensor when the 5 V reference circuit is the actual fault
- Replacing the ABS module
- Replacing the ignition/start switch for the associated no-start symptom
Troubleshooting steps
1.Confirm the low signal on a scan tool
The BPP PID reading zero or a fixed minimum through full pedal travel confirms the circuit fault rather than a mechanical issue.
2.Check the 5 V reference at the sensor
Key on, verify approximately 5 V on the supply terminal; a missing reference can also fault other sensors sharing that feed.
3.Measure the signal wire voltage
Back-probe the signal terminal; near 0 V with the sensor connected and disconnected points to a harness short to ground.
4.Isolate the short
Disconnect the sensor and the module connector, then ohm the signal wire to ground; repair the chafe if continuity to ground exists.
5.Substitute-test the sensor
If supply and wiring test good but the output stays low, replace the sensor and perform the required zero-point relearn.