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P2138 — Accelerator Pedal Position Sensor D/E Voltage Correlation

Severe

Quick answer

P2138 means the two redundant sensors inside the accelerator pedal disagree about pedal position. First move: inspect the pedal connector and harness (footwell damage, spills, rodents); the pedal assembly is one sealed part and is replaced as a unit when it fails.

What it means

Drive-by-wire throttles have no cable — your pedal is a sensor, the throttle is a motor, and software connects them. Because that link is safety-critical, both the pedal and the throttle carry TWO position sensors each, cross-checked constantly. P2138 sets when the two redundant sensors inside the accelerator pedal disagree about pedal position.

The computer responds defensively: reduced power (limp mode), high idle, or in some designs a near-dead pedal. Annoying, but it’s the system refusing to guess about your throttle.

Causes are narrow by design: the sensor pair itself (sold as part of the throttle body or pedal assembly), the connector, or the wiring between. There’s no five-dollar sensor here — but there’s also no mystery.

Common causes

Ordered from most to least likely.

  1. 1.

    Failed sensor pair in the pedal assembly

    The most common outcome; the assembly is replaced as a unit.

  2. 2.

    Connector problems (corrosion, spread pins, moisture)

    Check before buying the assembly — especially after footwell spills or engine washes.

  3. 3.

    Chafed or damaged wiring between pedal/throttle and ECM

    Wiggle-test while watching both sensor signals.

  4. 4.

    Carbon-bound throttle plate (P2135 cases)

    A sticking plate can break correlation; cleaning is the free first attempt.

How to diagnose it, step by step

Cheapest and most likely checks first.

  1. 1 Confirm the symptom pattern

    Limp mode plus this code is consistent; note whether it’s constant or appears with vibration/temperature (intermittent wiring clue).

  2. 2 Inspect connector and wiring

    At the pedal: check for crushed wiring, drink spills, floor mats interfering, rodent damage.

  3. 3 Watch both sensor signals

    On a scanner showing both channels, sweep slowly: the two traces should move in their designed relationship without dropouts. A glitch in one channel identifies the failing element.

  4. 4 Replace the pedal assembly if signals diverge

    The assembly is one sealed unit; when one sensor inside drifts, replacement is the repair. Perform any required pedal relearn afterward.

Parts & tools you may need

  • OBD-II scanner (code reader with freeze frame / live data)
  • Digital multimeter
  • Replacement accelerator pedal assembly (if condemned)
  • Electrical contact cleaner

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Related codes

Frequently asked questions

Can I drive with P2138?
In limp mode, technically — but reduced power on highway ramps is its own hazard. Treat correlation codes as promptly-fix items; they’re the throttle system’s integrity check.
Why did the computer cut my power?
Because it can no longer verify what the throttle/pedal is doing, and the failure mode of guessing wrong is unintended acceleration. Limp mode is the deliberately boring alternative.
Can I just clear the code?
It will return — correlation is checked continuously. Clearing is only useful to confirm a repair.