Short answer
P0123 sets when the TPS A voltage is higher than the normal upper limit. OBD-Codes.com flags over 4.65 V with the key on and engine off as a problem (your threshold may differ). Causes: a sensor not mounted securely, a short to another wire, a faulty sensor, or a damaged computer. Check the sensor ground first: a poor ground pulls the signal high.
- Code
- P0123
- Generic title
- Throttle Position Sensor/Switch A Circuit High Input
- Meaning
- The signal voltage is too high, often a lost ground or a short to voltage.
- Severity
- Medium to high
What P0123 means
OBD-Codes.com describes the sensor as a potentiometer on the throttle body and says P0123 sets when the computer sees a voltage higher than the normal upper limit, noting over 4.65 V key on, engine off as a sign of a problem. Your vehicle’s limit and test conditions are in its service manual.
Symptoms
- Rough idle
- High idle
- Surging
- Check engine light
Causes
P0123 causes, per OBD-Codes.com
| Cause | How to check |
|---|---|
| Sensor not mounted securely | Sensor sits flat and its drive engages the shaft |
| Lost or poor sensor ground | Back-probe the ground with the black lead on battery negative: near zero is good |
| Signal shorted to another wire | Trace the harness for rubbing and melted insulation |
| Faulty sensor | High signal with good reference and ground |
| Damaged computer | Only after the circuit checks out |
How to diagnose P0123
Check service bulletins
OBD-Codes.com suggests starting with technical service bulletins for your vehicle.
No symptoms? Clear and watch
Clear the code and see if it returns. Some high input codes are one-off glitches.
Trace the wiring
Follow each wire from the sensor connector, looking for breaks, rubbing and contact with other components.
Test ground and signal
Check the ground drop, then the signal voltage against your service manual.
Repair and relearn
Fix the fault, clear the code, and run any relearn.
More: how to test a TPS sensor, P0122 (low input), and the codes hub.
Questions people ask
Can I just clear P0123?
If there are no symptoms, OBD-Codes.com suggests clearing it and seeing if it comes back. If it returns, or the car idles high or surges, trace the wiring.
Why would a bad ground cause a high reading?
The sensor output sits between its reference and its ground. If the ground connection is poor, the whole range floats upward and the signal can read high even at closed throttle.
What is the difference between P0122 and P0123?
P0122 is voltage too low (often an open or a short to ground). P0123 is voltage too high (often a lost ground or a short to voltage).
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.