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P1639

Accelerator Pedal Position Sensor 1/2 Range Performance.

  • Volkswagen
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
6
AreaComputer and output circuits
39
FaultThe specific fault in that area

What it means

On Volkswagen, P1639 means the engine control unit has found that the two accelerator pedal position sensor signals do not agree with each other within the expected range. The pedal module uses two sensor tracks that should follow each other in a fixed relationship, and the control unit compares them constantly. If the difference is too large or the pattern is implausible, it sets the code and usually limits engine response as a safety measure.

Symptoms

  • Engine warning light on, and sometimes the electronic power control light as well
  • Car goes into limp mode with reduced power
  • Poor or delayed throttle response
  • Engine stuck at a raised or fixed idle speed
  • Cruise control not working
  • Hesitation or surging when pulling away

Possible causes

  • Faulty accelerator pedal module with a worn or drifting sensor tracklikely
  • Damaged wiring, chafed insulation or corroded pins in the pedal sensor circuitlikely
  • Poor connection or contamination at the pedal module plug or engine control unit connectorpossible
  • Fault in the shared sensor supply voltage or earth feeding the pedal sensorspossible
  • Moisture or water ingress into the pedal module or its connectorpossible
  • Internal fault in the engine control unitrare

How to diagnose

  1. Read all stored codes and freeze frame data, and note whether other pedal, throttle or supply voltage codes are present
  2. Inspect the pedal module, its plug and the footwell wiring for damage, moisture, corrosion or bent pins
  3. View live data for both pedal sensor values and sweep the pedal slowly from rest to full travel, looking for dropouts, jumps or values that do not track each other
  4. Check that the pedal returns freely and that nothing, such as a mat, is fouling the pedal travel
  5. Wiggle-test the harness and connector while watching live data to find intermittent faults
  6. Measure the sensor supply voltage and earth at the pedal connector against the wiring diagram for the specific model
  7. Check the wiring continuity and resistance between the pedal connector and the engine control unit for each sensor signal
  8. Clear the code and road test, checking whether it returns and under what pedal position

How to fix

  • Replace the accelerator pedal module if the sensor signals are erratic or do not correlate
  • Repair or replace damaged wiring sections, and clean or renew corroded terminals
  • Refit or replace faulty connectors and ensure they are fully locked and dry
  • Correct supply or earth faults found in the circuit, tracing the root cause
  • Carry out any required basic setting or adaptation of the pedal and throttle after the repair, as specified for the model
  • Have the engine control unit tested and repaired or replaced only after all wiring and pedal checks have passed

Can I keep driving?

Medium severity

The car can usually be driven gently to a workshop, but power may be limited and throttle response unpredictable, which can be unsafe in traffic or when overtaking. Get it checked soon and avoid driving if the engine is surging or not responding reliably.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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