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P0121Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance

What it means

The throttle or pedal position sensor signal is electrically possible, but it doesn't make sense compared with other sensors or with what the engine is doing. The throttle or pedal position sensor measures how far the throttle (or the accelerator pedal) is open.

Symptoms

  • Limp mode with very limited power
  • Hesitation, surging or erratic idle
  • Electronic throttle warning light

Common causes

  • Worn track in the sensor (dead spot)
  • Dirty or sticking throttle body
  • Throttle not learned after cleaning or replacement
  • Poor connection

What to check first

  1. Graph the two throttle position signals while opening slowly: they should be smooth and mirror each other
  2. Clean the throttle body and run the relearn procedure
  3. Check the connector pins and the 5 V reference
Can I drive with P0121? Not recommended. P0121 can lead to stalling, limp mode or engine damage; diagnose it before driving further.

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

How to test the parts behind P0121

Throttle and accelerator pedal position sensorsWiring, typical values, multimeter and scope tests

Known engine problems that set P0121

Volvo 5-cyl petrol: Electronic throttle module failure (older cars)Volvo, Ford · typically 80,000–180,000 km

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P0121: questions and answers

What does P0121 mean?

P0121: Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance. The throttle or pedal position sensor signal is electrically possible, but it doesn't make sense compared with other sensors or with what the engine is doing. The throttle or pedal position sensor measures how far the throttle (or the accelerator pedal) is open.

What are the symptoms of P0121?

Limp mode with very limited power. Hesitation, surging or erratic idle. Electronic throttle warning light.

What causes P0121?

Worn track in the sensor (dead spot). Dirty or sticking throttle body. Throttle not learned after cleaning or replacement. Poor connection.

How do you diagnose P0121?

1. Graph the two throttle position signals while opening slowly: they should be smooth and mirror each other 2. Clean the throttle body and run the relearn procedure 3. Check the connector pins and the 5 V reference

Can I drive with P0121?

Not recommended. P0121 can lead to stalling, limp mode or engine damage; diagnose it before driving further.