What it means
The ECU detects a general electrical fault on the throttle position sensor/switch A circuit. Signal missing, implausible, or wiring broken. Generic catch-all when no more specific TPS-A code applies.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
Throttle position sensor A reports throttle position to the engine control module, which uses the signal to manage engine response and compare it with other control inputs. P0120 sets when the A circuit has a general electrical or plausibility fault that does not fit a more specific low, high, or intermittent condition.
Common causes
Most likely first.
- TPS worn or failed (dead spot in resistive track)
- TPS wiring or connector fault
- TPS mechanically misaligned to throttle shaft
Symptoms
- Check engine light on
- Reduced throttle response, possible limp mode
- Hesitation or surging
- Idle too high or too low
How to diagnose it
- Record freeze-frame data and check live throttle position A while the throttle is moved gradually, noting missing, implausible, or erratic readings.
- Inspect the throttle position sensor A connector and wiring for looseness, corrosion, chafing, or damage.
- Check that the sensor and throttle body are seated and aligned correctly, without assuming an adjustment unless the manufacturer's procedure allows it.
- Compare sensor A with any redundant throttle or pedal position readings to see whether the disagreement is isolated to this circuit.
- Test the sensor's reference, ground, signal circuit, and sensor response against the manufacturer's specification.
Common fixes
- Reconnect or clean a loose or corroded TPS A connector.
- Repair damaged TPS A wiring or restore a poor circuit connection.
- Correct sensor alignment if it is adjustable and out of position.
- Replace the throttle position sensor if its signal remains faulty during testing.
Can I keep driving?
Throttle response may be limited or unpredictable, and the vehicle may enter limp mode. Avoid fast traffic and unnecessary driving; stop if throttle control becomes unreliable.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.