Why does my car go into limp mode with P0120?

The computer relies on the throttle and pedal signals to know what you ask for. When one fails a plausibility check, it limits power so the engine cannot accelerate on its own, which is a safety response.

Is P0120 the throttle body or the pedal?

It can be either, because the code covers throttle or pedal sensor A on the reporting car. A scan tool showing the live values for both helps to tell which one is jumping or stuck.

Will cleaning the throttle body fix P0120?

Sometimes, if carbon is restricting the plate. It will not help a worn sensor track or a broken wire, and many cars need a relearn after cleaning, so a clean without the relearn can leave the code or a rough idle.

How is P0120 different from P0122 and P0123?

P0122 and P0123 are the low and high voltage versions of the same sensor circuit. P0120 is the general circuit fault that some cars set when they do not report whether the signal is high or low.

P0120: Throttle/Pedal Position Sensor/Switch A Circuit

Quick Answer

Not safe to drive

P0120 means the engine computer found a fault in the throttle or accelerator pedal position sensor A circuit. On a modern drive-by-wire car there is a sensor at the throttle body and one in the pedal, each usually with two tracks that must agree, so the fault can be in either. The code names the circuit, not the part: the sensor, its connector and wiring, a dirty or worn throttle body, or rarely the engine computer. Many drive-by-wire cars cut power or limit speed when it sets.

Severity: Moderate · Electrical

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What does P0120 mean?

P0120 is a electrical-related diagnostic trouble code classified as moderate severity.

What are the symptoms of P0120?

Check engine light on, sometimes with an engine or throttle warning symbol
Limp mode with reduced power or a speed limit
Hesitation or flat spots when pressing the pedal
Unstable or fixed high idle
Stalling or refusing to rev
Stability control or traction warnings coming on, as seen on some cars

What causes P0120?

Worn or failing throttle body or pedal position sensor
: high
Corroded, loose or damaged connector at the throttle body or pedal
: high
Chafed or broken wiring, or a bad 5 volt reference or ground
: medium
Carbon build-up restricting the throttle plate or a weak throttle motor
: medium
Throttle body not relearned after cleaning or replacement
: low
Engine computer fault (rare)
: low

Is it safe to drive with P0120?

No - address this immediately. Treat it as unsafe for normal driving. The engine computer may limit power or road speed, hold a fixed idle or cut power when you press the pedal, which makes joining fast roads and overtaking risky. Drive slowly to a safe place or workshop with the hazard lights if needed, and have the car towed if it will not accelerate properly.

How do you diagnose P0120?

Read all stored codes and the freeze frame. Look for a second throttle, pedal or P2135 type correlation code, because a pair of codes points to one of the two sensors agreeing badly with the other.
Check that nothing blocks the pedal, such as a floor mat, and that the pedal moves smoothly.
Inspect the throttle body and pedal connectors for corrosion, pushed-back pins and oil. Flex the plug and harness gently while the ignition is on to catch an intermittent break.
Watch the throttle and pedal position values on a scan tool. They should rise smoothly and without jumps from closed to fully open, and the two sensor tracks should move together. A value stuck, jumping or reading zero names the sensor circuit at fault.
Check the 5 volt supply, signal and ground at the suspect connector with a multimeter, using the wiring diagram for that car. A missing reference points to wiring or the computer, not the sensor.
Remove carbon from the throttle body if it is dirty, without forcing the plate, then repeat the check. Many cars need a relearn after cleaning or replacement.
Replace the part that fails the test, carry out the throttle basic setting or idle relearn the car needs, clear the code and road-test. A generic OBD2 reader shows the code and live throttle values but cannot run the relearn on many cars.

How much does P0120 cost to fix?

Repair	Parts Cost	Labor Cost	Total Estimate	DIY Difficulty
Clean and reseat throttle body or pedal connector	€0–€10	€0–€40	€0–€50	Easy
Clean throttle body	€5–€15	€30–€90	€35–€105	Moderate
Replace accelerator pedal sensor assembly	€40–€200	€30–€90	€70–€290	Moderate
Replace electronic throttle body assembly	€150–€600	€60–€180	€210–€780	Professional
Repair damaged wiring or connector pins	€10–€40	€60–€180	€70–€220	Moderate

Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.

Common questions about P0120

What does P0120 mean?: P0120 means the engine computer saw a fault in circuit A of the throttle or pedal position sensor. It is a circuit code: the sensor, its connector, its wiring or the throttle body can all be the cause.
Why does my car go into limp mode with P0120?: The computer relies on the throttle and pedal signals to know what you ask for. When one fails a plausibility check, it limits power so the engine cannot accelerate on its own, which is a safety response.
Is P0120 the throttle body or the pedal?: It can be either, because the code covers throttle or pedal sensor A on the reporting car. A scan tool showing the live values for both helps to tell which one is jumping or stuck.
Will cleaning the throttle body fix P0120?: Sometimes, if carbon is restricting the plate. It will not help a worn sensor track or a broken wire, and many cars need a relearn after cleaning, so a clean without the relearn can leave the code or a rough idle.
How is P0120 different from P0122 and P0123?: P0122 and P0123 are the low and high voltage versions of the same sensor circuit. P0120 is the general circuit fault that some cars set when they do not report whether the signal is high or low.

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