P0123: The throttle position sensor voltage is too high
Throttle/Pedal Position Sensor/Switch A Circuit High Input
The throttle position sensor reads stuck at wide open. This can cause surging, high revs or a sudden fuel cut. Stop driving and have it checked before you drive again.
Stop driving and get help if
- The check engine light is flashing
- The temperature gauge runs high, or you see steam (overheating)
- The car loses power, hesitates badly or stalls
- You smell burning or see smoke
- A brake warning light comes on, or the brakes feel different
Pull over as soon as you can, turn the engine off, and call a tow or roadside help.
What it means
P0123 means the TPS signal voltage is above the maximum the ECM expects. A sensor stuck high tells the computer the throttle is fully open even at idle. The ECM may cut fuel to prevent a runaway condition, or the engine may surge unexpectedly. The most common electrical cause is a short to the 5V reference line or an internally failed sensor with an open circuit that floats toward the supply voltage.
Common causes
- Failed TPS sensor with internal open circuitAn open internal circuit floats the output toward 5V, which reads as wide-open throttle.
- Short to 5V reference in the signal wireA chafed signal wire touching the reference wire holds the output high regardless of actual position.
- Damaged connector bridging signal and reference pinsA melted or bent connector can allow the signal pin to contact the 5V pin.
What the fix could involve
From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.
- TPS replacement (cable)
- Electronic throttle body
- Wiring repair
Symptoms
- Check engine light on
- High idle or engine surging
- Transmission shifting very aggressively or not at all
- Engine may stall from fuel cutoff at idle
- Possible runaway RPM if the ECM does not intervene
What to do next
Do not attempt to drive this vehicle. Disconnect the TPS connector and check whether signal voltage drops toward zero with the sensor unplugged. If it does, the sensor is shorted internally to its own reference. If voltage stays high with the sensor disconnected, the wiring has a short to the 5V supply line. Replace the sensor or repair the wiring accordingly.
Lewis shows the live throttle position reading so you can see whether it is pinned high or only jumps at certain pedal positions. Get Lewis on the App Store or Google Play.
Related codes
FAQ
- Can P0123 cause unintended acceleration?
- On older cable-throttle vehicles, a stuck-high TPS mostly causes ECM logic problems rather than actual physical acceleration. On drive-by-wire, the ECM typically detects sensor conflict and defaults to idle or limp mode rather than commanding wide-open throttle.
- Why does the engine stall with P0123 if the sensor says throttle is wide open?
- The ECM cuts fuel when it detects an implausible wide-open throttle signal at zero engine demand. It is a safety response to prevent uncontrolled acceleration.
- Does P0123 affect the fuel trims?
- Yes. A TPS stuck high makes the ECM think the engine needs maximum fuel all the time, driving fuel trims toward rich and causing misfires from flooding.
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