Engine

P0123 — Throttle/Pedal Position Sensor A Circuit High Input

Severity: medium Drive with care, to a shop

What P0123 means

The engine control unit constantly monitors the signal voltage from the throttle position sensor (TPS) or accelerator pedal position (APP) sensor. It normally rises smoothly from a low value at idle to a high value at wide-open throttle. P0123 is set when that signal goes above the allowed range, for example from an open sensor ground, a signal wire shorted to power, or a failed sensor.

Symptoms

  • Check Engine light on
  • Erratic or unresponsive acceleration
  • Rough or high idle
  • Reduced power or limp mode
  • Hesitation or stumbling when pressing the pedal
  • Stalling at idle or when lifting off the throttle
  • Reduced power warning on the dash

Possible causes

  1. Failed throttle position or accelerator pedal position sensor
  2. Open sensor ground or signal wire shorted to voltage
  3. Damaged wiring harness or connector
  4. Corroded terminals or poor connection
  5. Dirty or sticking throttle body
  6. Rarely, a fault in the PCM input circuit

How to diagnose

  1. Scan for codes and freeze-frame data and look for related throttle, pedal or 5 V reference codes
  2. Inspect the sensor connector and harness for damage, moisture, corrosion or chafing
  3. With a scan tool, watch throttle or pedal percentage at key on and idle: it should be near zero and rise smoothly
  4. Use a multimeter to check the 5 V reference and the sensor ground
  5. Test the signal wire for a short to power or an open circuit
  6. Inspect the throttle plate, clean it if needed and check that it moves freely
  7. Sweep the pedal slowly and watch the signal for spikes or dropouts
  8. If wiring and sensor test fine, check PCM power and the PCM itself

Common fixes

  • Replace the throttle position or accelerator pedal sensor
  • Repair the wiring or replace the connector, fixing the short or open ground
  • Clean the throttle body and perform a throttle relearn
  • Replace the throttle body assembly if the sensor is built in
  • As a last resort, diagnose, reflash or replace the PCM

Questions and answers

Can I drive with a P0123 code?

Only briefly and carefully, such as to a repair shop. The engine may enter limp mode or stall, so don't put off the repair.

What most often causes P0123?

Most often it's a failed throttle or pedal position sensor, an open ground, or a damaged connector. Check the wiring and connector before replacing parts.

Will cleaning the throttle body fix P0123?

Sometimes, if the plate is sticking from carbon buildup. If the cause is electrical, such as the sensor or wiring, cleaning won't clear the code.

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.