P2138: The two accelerator pedal position sensors do not agree
Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation
The two accelerator pedal position signals disagree, so the car usually cuts power into limp mode. Get it checked today and stay off highways. If the pedal stops responding, pull over.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
Like the throttle body, the accelerator pedal on a drive-by-wire system has two position sensors that must agree. P2138 means they do not. The car cannot tell reliably how far you are pressing the pedal, so it limits throttle as a safety measure. P2138 is the pedal version of P2135; if both codes appear, suspect the wiring harness or connector that feeds both pedal and throttle sensors. If only P2138 appears, the issue is at the pedal itself. Accelerator pedal assemblies are relatively affordable to replace and do not require programming on most vehicles.
Common causes
- Failed accelerator pedal position sensor assemblyThe dual sensors in the pedal assembly wear out. The whole pedal assembly is replaced as a unit.
- Damaged or corroded connector at the pedalThe connector under the dash near the pedal can corrode from moisture.
- Damaged wiring harness near the pedalWires can be pinched or chafed near pedal pivot points.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- Accelerator pedal connector cleaning
- Accelerator pedal assembly replacement
Symptoms
- Limp mode or reduced power mode
- Poor or delayed throttle response
- Vehicle will not accelerate normally
- Check engine light on
What to do next
Locate the accelerator pedal connector under the dash, unplug it, and inspect for corrosion or damaged pins. Clean the contacts and reconnect. If the code returns, replace the pedal assembly. On most vehicles this is a straightforward DIY repair: three or four bolts and one connector. No programming is needed for the pedal on most platforms.
Lewis reads P2138 alongside any related pedal and throttle sensor codes, so you can see whether the fault points to the pedal or to the shared wiring. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- Is the pedal the only thing I need to replace?
- If only P2138 is set and no P2135, then the pedal assembly is the most likely fix. If P2135 is also set, inspect the shared wiring harness.
- Does the new pedal need programming?
- On most vehicles, no. The PCM reads the raw voltage and compares the two signals. Plug in the new assembly and it works.
- How do I access the pedal connector?
- It is under the dash near the firewall. You may need to remove a kick panel or reach underneath. A flashlight will show it clearly.
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