P0121: Throttle or pedal position sensor A: out of expected range
The signal from throttle or pedal sensor A does not match what the ECU expects. Usually dirt, a worn sensor or a poor electrical contact.
| Code | P0121 |
|---|---|
| System | Engine and transmission |
| Group | P01xx, Air and fuel metering |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0121 means
The ECU needs to know how far the throttle valve (the flap that lets air into the engine) is open, or how far you are pressing the accelerator, to meter air and fuel. Which sensor counts as sensor A is decided by each manufacturer, although it is usually the throttle one. Here there is a signal, but it does not agree with other data, such as the air flow or the sensor’s second track.
Most common causes
- Throttle body clogged with carbon, so it does not open or close as it should
- Throttle not relearned after cleaning or removal
- Intermittent or corroded contact in the sensor connector
- Worn sensor track giving erratic readings at some positions
- Air leak so the air entering does not match the throttle opening
- Faulty throttle body or sensor
Symptoms
- Engine warning light on
- Limp mode with little power
- High, low or unsteady idle
- Sluggish or jerky response when accelerating
Can you drive with P0121?
With care You can drive, but the car may suddenly lose power when it drops into limp mode. Get it to a garage soon and avoid overtaking and fast roads in the meantime.
Open the bonnetthe in-depth explanation
How to check it
Watch the throttle position in live data at idle and while pressing the pedal slowly: it should rise without jumps and always return to the same value when released. If you clean the throttle body, ask the garage about a relearn, as many cars need one afterwards.
How to read and clear P0121 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0121 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P011D Charge air and intake air temperatures on bank 2 do not agree
- P011E Coolant temperature 1 and outside air temperature do not match with the engine
- P011F Coolant temperature 2 and outside air temperature do not match with the engine
- P0120 Throttle or pedal position sensor A: circuit fault
- P0122 Throttle or pedal position sensor A: low signal
- P0123 Throttle or pedal position sensor A: high signal
- P0124 Throttle or pedal position sensor A: intermittent signal
- P0125 Engine takes too long to warm up for fuel mixture control
- P0100 Mass or volume air flow sensor circuit fault
- P0101 Air flow sensor range or performance problem
- P0102 Air flow sensor circuit low input
- P0103 Air flow sensor circuit high input
What does code P0121 mean?
The ECU needs to know how far the throttle valve (the flap that lets air into the engine) is open, or how far you are pressing the accelerator, to meter air and fuel. Which sensor counts as sensor A is decided by each manufacturer, although it is usually the throttle one. Here there is a signal, but it does not agree with other data, such as the air flow or the sensor’s second track.
Can you drive with P0121?
You can drive, but the car may suddenly lose power when it drops into limp mode. Get it to a garage soon and avoid overtaking and fast roads in the meantime.
How do you clear P0121?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0121 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
