Short answer
P0122 sets when the TPS A signal voltage is below the computer’s lower limit; OBD-Codes.com notes some vehicles set it at 0.17 to 0.20 V. Causes: a sensor not mounted securely, a short to ground or to another wire, a faulty sensor, or a damaged computer. Check the 5 V reference and the signal wire before replacing the sensor.
- Code
- P0122
- Generic title
- Throttle Position Sensor/Switch A Circuit Low Input
- Meaning
- The signal voltage is too low, often an open or a short to ground.
- Severity
- Medium to high
What P0122 means
OBD-Codes.com describes P0122 as the computer detecting that throttle position sensor A is reporting too low a voltage, with some vehicles setting it at 0.17 to 0.20 V. Your vehicle’s threshold and test conditions are in its service manual.
Symptoms
- Rough or low idle, or a very high idle
- Stalling
- Surging
- Little or no acceleration
- Check engine light
Causes
P0122 causes, per OBD-Codes.com
| Cause | How to check |
|---|---|
| Sensor not mounted securely | Sensor sits flat and its drive engages the shaft |
| Signal shorted to ground or another wire | Inspect the harness; check for continuity to ground with the plug off |
| Lost 5 V reference | Back-probe the reference: expect about 5 V |
| Faulty sensor | Signal low with good reference and ground |
| Damaged computer | Only after the circuit checks out |
How to diagnose P0122
Inspect
Check the sensor, connector and wiring for breaks, rubbing and corrosion. Confirm the sensor is seated.
Check the reference
Key on, back-probe the reference wire. About 5 V is normal. Missing reference is a wiring or computer issue.
Check the signal
Back-probe the signal and compare it with the service manual. Too low with good reference and ground means a bad sensor.
Hunt intermittents
If the code comes and goes, check the harness for rubbing and grounding issues while wiggling it.
Repair and relearn
Fix the fault, clear the code, and run any relearn.
More: how to test a TPS sensor, how to adjust one, P0123 (high input), and the codes hub.
Questions people ask
Can a loose TPS cause P0122?
Yes. OBD-Codes.com lists a sensor that is not mounted securely as a cause, and a reader tip there says the code can follow a sensor that was not rotated correctly as it was installed. Check the fit after any replacement.
Why did P0122 appear right after I replaced the TPS?
The sensor may not be seated on the throttle shaft, may need adjusting if it is an adjustable type, or may be the wrong part. Also check that the connector clicked fully home.
Does P0122 mean the sensor is dead?
Not necessarily. A broken reference wire or a signal wire shorted to ground gives the same code with a perfectly good sensor. Test before you buy.
Sources
Last reviewed 2026-10-12. General guidance only: specs, procedures and fitment vary by vehicle, so confirm in your service manual and on the listing before you buy or wrench.