What P0123 means
P means powertrain (engine and transmission). The 0 marks a generic code defined by SAE, so the same number means the same thing across makes. The third character, 1, places it in the fuel and air metering subsystem; the last two digits identify the specific fault.
In the standard's wording this code family covers throttle position sensors and, on electronic throttle ("drive-by-wire") vehicles, accelerator pedal position sensors. Electronic throttle systems use at least two signals for each so the module can cross-check them; "A", "B" and "C" identify which signal is at fault, and the assignment is set by the manufacturer.
What “Circuit High” means here
"High" means the signal or control voltage rose above the maximum the module expects. On a three-wire sensor fed by a 5 V reference, typical causes are a signal wire shorted to the reference or to battery voltage, an open sensor ground, or a failed sensor.
What you may notice
Symptoms depend on the vehicle and on how the module responds to the fault. Any of these can accompany P0123:
- Reduced power or a limp-home mode with limited throttle
- Hesitation or surging
- Erratic or high idle
- Harsh or delayed gear changes on automatic transmissions
Where to start diagnosing P0123
- Identify from the vehicle's service information whether the "A/B/C" signal is on the throttle body or the pedal assembly.
- Inspect the connector and harness at that component; flex the wiring while watching live data.
- Sweep the throttle or pedal slowly and watch for dropouts or jumps in the position signal.
- On electronic throttles, check the throttle body for carbon build-up that can cause position disagreement.
Clear the code only after recording freeze frame data: it shows the engine speed, load and temperature at the moment the fault set, which is often the best clue to reproducing it.
Live data to watch
These standard OBD2 values relate to P0123. Support varies by vehicle; a value your car does not report will simply be missing.
| Value | What to look for |
|---|---|
| Throttle position (PID 0x11) | Should move smoothly from closed to open with no steps or dropouts. |
| Absolute throttle position B/C (PIDs 0x47–0x48) | The paired signal should track the first one consistently. |
| Accelerator pedal position D/E (PIDs 0x49–0x4A) | Both pedal signals should move together when the pedal is pressed. |
Related codes
Codes from the same throttle / pedal position sensor family. If several are stored together, the shared part — wiring, a common reference voltage, or the component itself — is the place to start.
| Code | Definition |
|---|---|
| P0120 | Throttle/Pedal Position Sensor/Switch "A" Circuit |
| P0121 | Throttle/Pedal Position Sensor A Circuit Range/Performance |
| P0122 | Throttle/Pedal Position Sensor/Switch "A" Circuit Low |
| P0124 | Throttle/Pedal Position Sensor/Switch "A" Circuit Intermittent |
| P0220 | Throttle/Pedal Position Sensor/Switch "B" Circuit |
| P0221 | Throttle/Pedal Position Sensor/Switch "B" Circuit Range/Performance |
| P0222 | Throttle/Pedal Position Sensor/Switch "B" Circuit Low |
| P0223 | Throttle/Pedal Position Sensor/Switch "B" Circuit High |
Further reading
Frequently Asked Questions
What does P0123 mean?
P0123 is the generic SAE J2012 code for "Throttle/Pedal Position Sensor/Switch "A" Circuit High". In plain terms, it means the engine computer has detected a "circuit high" fault on the throttle / pedal position sensor.
Can I keep driving with P0123?
Throttle and pedal faults can trigger reduced-power mode without warning. Drive cautiously and avoid situations where you need sudden acceleration until it is repaired.
What should I check first for P0123?
Identify from the vehicle's service information whether the "A/B/C" signal is on the throttle body or the pedal assembly.
Definition source: SAE J2012 / ISO 15031-6 generic DTC definitions. This is the generic meaning that applies across makes; a manufacturer can define a code more narrowly or add its own sub-codes, so confirm against the service information for your vehicle before replacing parts. Written by the OBDAssistant engineering team — see our editorial policy.