What does it mean?
P1631 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Acceleration Pedal Position Sensor 1 Signal Too High .
Symptoms
- MIL (check engine lamp) on with a reduced power warning
- Pedal reads as applied when the driver's foot is off it, or engine revs hang high
- Engine refuses to rev at all as a protective response, or will not idle down
- Cruise control unavailable
- Erratic throttle response and surging
- Occasional stall when coming to a stop
Likely causes
- Signal wire shorted to battery positive or to the 5 V reference
- Open or high-resistance sensor ground, which drives the signal high
- Corrosion bridging pins inside the pedal connector after water entered the footwell
- Internal sensor failure with the resistive track shorted to its supply
- Harness chafed under the dash or through the bulkhead and touching a power feed
- Incorrect pedal assembly fitted, with a different pin arrangement
- Module input circuit fault, the least likely cause
How to fix it
- Read both pedal sensor voltages with the pedal fully released; sensor 1 should sit at its low rest value, not near the reference level
- Unplug the pedal connector; if the reported voltage stays high, the fault is in the harness or the module, not the sensor
- Check the sensor ground for continuity and voltage drop, since an open ground is a classic cause of a high reading
- Test the signal wire for a short to the 5 V reference and a short to battery positive
- Inspect the connector for corrosion, water, bent or backed-out pins
- Replace the accelerator pedal assembly once the harness has tested good
- Run the pedal adaptation and confirm both signals track correctly through the full range