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DTC codes / P21xx · Fuel and air metering / P2123

P2123Accelerator Pedal Position Sensor D Circuit High

P2123 means the engine computer has detected an abnormally high voltage on the circuit for accelerator pedal position sensor D, which is one of the redundant signals used to determine how far the driver is pressing the pedal. The computer compares this signal against the other pedal sensor circuits and sets the code when sensor D's voltage exceeds the expected range, often putting the vehicle into a reduced-power limp mode.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • The accelerator pedal may feel unresponsive or the engine may idle at a raised speed without input
  • Reduced engine power or limp mode with a noticeably limited top speed
  • The electronic throttle control warning light or check engine light illuminated
  • Hesitation or a stumble when pressing or releasing the accelerator pedal
  • Often no symptoms besides the warning light if the fault is intermittent

Common causes, most likely first

  1. A faulty accelerator pedal position sensor assembly, where the internal sensor D track wears or fails
  2. Corroded, bent, or pushed-back pins in the accelerator pedal sensor connector
  3. A chafed or open signal wire between the pedal sensor and the engine control module
  4. Water intrusion into the pedal sensor connector or housing causing a high-resistance short
  5. A poor ground connection shared by the pedal sensor circuits
  6. A rare internal fault in the engine control module's sensor reference or signal circuit

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data for P2123 before clearing anything
  2. Inspect the accelerator pedal connector and harness for corrosion, water, or loose pins
  3. Back-probe the sensor D signal wire and compare its voltage to the other pedal sensor signals through the full pedal travel
  4. Check the sensor ground circuit for excessive resistance with a voltage drop test
  5. Wiggle-test the harness while watching live pedal position data to expose an intermittent fault
  6. Replace the accelerator pedal position sensor assembly if its output is erratic or out of range
  7. Repair or replace damaged wiring and re-verify live data before returning the vehicle

What the pedal sensor D code hides

  • Sensor D is one of several redundant tracks inside the pedal assembly, so a single failed track can set P2123 while the pedal still feels normal to the driver.
  • A high-voltage code is frequently caused by a poor ground or a short to voltage rather than a dead sensor, so replacing the pedal first can be a costly misdiagnosis.
  • Water or spilled drinks reaching the pedal connector often create intermittent high-voltage readings that only appear on damp mornings or after a car wash.
  • The engine control module may substitute a default pedal position and limit power, so the vehicle can feel fine at idle yet refuse to accelerate normally.
  • Aftermarket floor mats or pedal covers that restrict full pedal travel can stress the sensor tracks and contribute to repeat failures.

Can I keep driving with P2123?

You can usually drive the vehicle to a repair shop, but expect reduced power and avoid highways or heavy traffic until the fault is repaired. If the pedal becomes completely unresponsive or the engine races, stop driving and arrange a tow.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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