From Ross-Tech Wiki
18047/P1639 - Accelerator Position Sensor 1/2 (G79/G185): Implausible Signal
- Malfunction Indicator Light (MIL) ON
- Reduced Engine Output
- Wiring and/or connections faulty
- Faulty ECM
- Faulty Accelerator Pedal
- Check Measuring Block Readings for Accelerator Pedal
- Check Voltage Signals from ECM to Throttle Pedal (see factory repair manual)
- Check Wiring and Connectors from Accelerator Pedal to ECM
- There are 2 sensors in the accelerator pedal, both measure the same except that they are working in opposite directions. This means one counts from 0 to 100, while the other one counts from 100 to 0.
- Accelerator Position Sensor faults can be caused by issues with the Oxygen Sensor(s) and it's wiring. Please verify this BEFORE replacing the ECM or Accelerator Pedal. Accelerator Pedal failure is very rare.