P2138
PowertrainThrottle/Pedal Pos Sensor/Switch D / E Voltage Correlation
The ECU has detected that the two throttle pedal position sensors aren't agreeing with each other. Modern drive-by-wire pedals have two redundant sensors for safety, when their values don't correlate within tolerance, this code sets and the car typically drops into limp mode.
ⓘ Information only. This page provides general educational information about fault code P2138. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P2138 mean?
P2138 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Throttle/Pedal Pos Sensor/Switch D / E Voltage Correlation.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light, often immediate after the discrepancy is detected
- • Limp mode, throttle response is severely restricted
- • Stalling at idle in some cases
- • Hesitation when pressing the accelerator
- • Cruise control disabled, the system requires healthy pedal sensors
- • Unstable idle
Possible causes
Causes commonly associated with P2138, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Failed pedal position sensor (one of the two redundant elements has gone bad)
- 2. Damaged wiring between pedal and ECU, six-wire pedal looms get knocked or kinked when carpets or panels are removed
- 3. Connector at the pedal contaminated, drinks spills or wet shoes can cause issues over time
- 4. Bent pedal mechanism after kerb-strike or collision
- 5. ECU fault, rare but possible on some models with known electronics issues
- 6. Wrong-spec aftermarket pedal box fitted on track-prepared cars
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read live data on both pedal position sensors simultaneously. Both should track from 0 to 100% smoothly with the accelerator pressed; values should always match within a few percent. If they diverge, the pedal is the fault
- 2. Inspect the pedal wiring and connector under the dashboard; six wires (two power, two ground, two signals) should all be intact and seated correctly
- 3. Check for moisture or damage at the connector
- 4. Disconnect and reseat the connector, sometimes a poor seat is enough to set the code
- 5. If pedal and wiring are clean, swap a known-good pedal if available, otherwise replace based on best evidence
Common questions about P2138
Why are there two pedal sensors? +
Safety. Drive-by-wire pedals control a lot through electronics rather than a physical cable. Two redundant sensors mean if one fails, the ECU can detect the disagreement and drop into limp mode (preventing unintended acceleration) rather than blindly trusting bad data. P2138 is specifically the disagreement code, the safety system has done its job.
Is the car safe to drive? +
In limp mode, yes, but throttle response is heavily restricted. Most drivers can manage a limp-home journey to a garage. Don't ignore this and try to clear the code; an actual disagreement between the sensors means one of them is genuinely faulty, and you don't want unpredictable acceleration.
Could a wet floor mat cause this? +
Yes, surprisingly often. Drink spills, wet boots, or damaged door rubbers can let water reach the pedal connector. Once moisture corrodes the connector pins, intermittent P2138s appear, sometimes only when the connector is warm or cold. Worth inspecting the connector before condemning the pedal itself.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →