P0121: Throttle or pedal position sensor A: out of expected range

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.

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 this same explanation and whether it’s confirmed, pending or permanent.

With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.

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 the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.

Similar codes

• P0117 Engine coolant temperature sensor circuit low
• P0118 Engine coolant temperature sensor circuit high
• P0119 Engine coolant temperature sensor circuit intermittent
• 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

P0121 is a generic code, so it means the same on any make, for example on Audi, Fiat, Kia, Mazda, Opel / Vauxhall, Toyota. See what Final OBD does on your car in makes and models.