P1639

Code

VOLKSWAGEN P — Powertrain

Accelerator Pedal Position Sensor 1/2 Range Performance

Brand: VOLKSWAGEN

Type: P — Powertrain

Views: UK: 40 EN: 114 RU: 48

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Page language: EN

Causes

Faulty accelerator pedal position (APP) sensor/module
Damaged wiring harness or connector (open, short to ground/voltage)
Poor battery or sensor supply/ground
Corroded or loose connector pins
Water/moisture ingress or mechanical damage to pedal assembly
ECM input circuit fault or intermittent ECU issue

Symptoms

Check Engine Light (MIL) illuminated
Reduced engine power / limp-home mode
Poor or unresponsive throttle response
Cruise control disabled
Intermittent or stuck pedal position reading on scan tool

What to check

Read freeze frame and live data with a capable scan tool; record APP sensor 1 and 2 voltages/percentages at rest and during pedal travel
Check battery voltage and relevant fuses/power supplies for the pedal module
Visually inspect pedal assembly, harness, and connector for damage, corrosion, or water ingress
Backprobing: measure APP sensor 1 and 2 reference, supply (typically 5 V) and ground, and compare to expected voltages
Wiggle test harness while watching live data to reveal intermittent faults
Check for related communication or ECU faults (CAN/ LIN if applicable)

Signal parameters

Typical APP sensor supply: ~5 V reference (check vehicle spec)
Typical sensor outputs: ~0.5–4.5 V across pedal travel (varies by model)
Both sensors should change smoothly and correlate; difference between sensors must remain within manufacturer tolerance
No sensor should be stuck at fixed voltage, jump erratically, or read open/short (0 V or battery voltage)
At rest (idle), one sensor often reads low (~0.5 V) and the other a different stable value—both should move monotonically with pedal

Diagnostic algorithm

Connect scan tool, read codes and freeze frame. Note APP1 and APP2 values and whether other codes are present.
With ignition on (engine off), monitor APP1/APP2 voltages/percent on the scan tool. Slowly press and release the pedal; verify smooth, continuous change and proper correlation.
Backprobe the pedal connector: confirm 5 V reference, ground continuity, and sensor output voltages match scan tool readings. Repair any missing reference or ground.
Inspect and repair any damaged wiring, pins, or corrosion. Perform wiggle test while observing live data to find intermittent faults.
If signals are out of range or inconsistent and wiring is good, remove pedal assembly and bench-test sensor resistances/voltages per service data. Replace pedal module if internal sensors fail.
After repair or replacement, clear codes and perform pedal/ECU adaptation or calibration procedure if required by manufacturer.
If faults persist after pedal replacement and wiring verification, consider ECU input diagnostics or module replacement as per workshop manual.

Likely causes

Wiring short or intermittent connection between pedal sensors and ECU
One sensor inside the pedal failed or has drifted out of range
Connector corrosion at pedal harness (common under carpet/wet areas)
Blown fuse or poor sensor supply voltage
ECU input stage fault (less common) or missing pedal module programming

Fault status

⚠️ Status

Accelerator Pedal Position Sensor 1/2 Range Performance — sensor outputs out of expected range or not correlating

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-2.5 hours

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P1639 — Accelerator Pedal Position Sensor 1/2 Range Performance