Engine

P2122 — Accelerator Pedal Position Sensor D Circuit Low

Severity: medium Drive with care, to a shop

What P2122 means

On a drive-by-wire car, the engine control module compares signals from several accelerator pedal position (APP) sensors to know what the driver wants. P2122 sets when the voltage in the sensor D circuit falls below the expected minimum, typically from an open, a short to ground or a failing sensor. Because the signals no longer agree, the ECM stops trusting the pedal and limits power.

Symptoms

  • Weak or no acceleration
  • Limp mode with limited rpm
  • Check Engine light on
  • Dead spot or hesitation in the pedal
  • Unstable or high idle
  • Electronic throttle warning light in some cars

Possible causes

  1. Failed accelerator pedal assembly
  2. Damaged wiring harness near the pedal or under the dash
  3. Corroded or loose pedal connector
  4. Signal wire shorted to ground
  5. Open or shorted 5 V reference circuit
  6. Rarely, a faulty ECM or throttle body

How to diagnose

  1. Read all codes and freeze frame data, then clear and see if P2122 returns
  2. With a scan tool, watch the pedal sensor signals live and compare them as you press the pedal slowly
  3. Inspect the pedal connector for corrosion, bent pins and poor fit
  4. Inspect the harness at the pedal and under the dash for chafing, moisture or damage
  5. Use a multimeter to check 5 V reference, ground and signal voltage at the connector
  6. Test the signal wire for a short to ground and for continuity to the ECM
  7. If wiring is good, replace the pedal assembly and perform any required relearn

Common fixes

  • Clean the connector and repair or replace damaged terminals
  • Repair or replace the shorted or broken section of wiring
  • Replace the accelerator pedal assembly
  • Clear codes and run a pedal or throttle relearn with a scan tool
  • Reflash or replace the ECM only if confirmed faulty

Questions and answers

What does P2122 mean?

It means the signal from accelerator pedal position sensor D is too low. The ECM sees voltage below the normal range and treats the pedal data as unreliable.

Can I drive with P2122?

Only carefully and to a repair shop. Power will be limited and pedal response may be unpredictable, which is risky in traffic.

What most often causes P2122?

Most often it is a worn or failed pedal assembly, or a poor connection or damaged wiring at the pedal connector and harness.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.