What it means
The TPS signal voltage is below the lower acceptable threshold. The ECU usually enters limp-home mode and limits engine torque while the fault is active.
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 or pedal position sensor A sends a position signal to the module, which monitors its voltage along with the sensor's reference and ground. P0122 sets when the A signal falls below the accepted lower limit, commonly because the signal is pulled toward ground or the sensor supply or sensor itself has failed.
Common causes
Most likely first.
- Signal wire shorted to ground
- TPS internally failed
- 5V reference voltage to TPS missing
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 sensor A input to confirm it is unusually low when the code is active.
- Inspect the sensor A connector and harness for a signal wire shorted to ground, damaged insulation, corrosion, or a loose terminal.
- Check whether the sensor's reference supply and ground are present and stable, using the manufacturer's wiring information.
- Test the signal wire for a short to ground and check the sensor response through its operating range against the manufacturer's specification.
- If other sensors sharing the reference supply also show faults, check the shared supply circuit before condemning sensor A.
Common fixes
- Repair a signal wire shorted to ground or damaged harness section.
- Restore a missing or poor 5-volt reference connection to the sensor circuit.
- Clean or repair a corroded or loose sensor connector.
- Replace throttle or pedal position sensor A if it fails circuit and response tests.
Can I keep driving?
The module may limit engine torque or enter limp mode, making acceleration unreliable. Avoid driving in situations that require quick acceleration, and stop if throttle response is lost.
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.