From Ross-Tech Wiki

18047/P1639 - Accelerator Position Sensor 1/2 (G79/G185): Implausible Signal

Possible Symptoms

  • Malfunction Indicator Light (MIL) ON
  • Reduced Engine Output

Possible Causes

  • Wiring and/or connections faulty
  • Faulty ECM
  • Faulty Accelerator Pedal

Possible Solutions

  • Check Measuring Block Readings for Accelerator Pedal
  • Check Voltage Signals from ECM to Throttle Pedal (see factory repair manual)
  • Check Wiring and Connectors from ECM to Accelerator Pedal

Special Notes

  • 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.