P0123: Throttle/Pedal Position Sensor/Switch A Circuit High

Common causes

• A failed throttle position sensor (on many cars it's built into the electronic throttle body and not sold separately)
• An open sensor ground wire or a poor ground connection
• The signal wire shorted to the 5-volt reference or another voltage source
• A loose, corroded or water-damaged connector

Code meanings can vary slightly by manufacturer. Use these as a starting point and confirm with your vehicle's service information or a mechanic before replacing parts.

Symptoms

• Check engine light, often with a reduced power or throttle warning
• Limited throttle response (limp mode)
• High or erratic idle, hesitation or stalling
• Harsh or odd shifting on automatics

Is it safe to drive?

If the car goes into reduced-power mode, stalls or surges, don't drive it in traffic; have it towed. If it drives normally with a steady light, get it checked soon.

How to check it with a scanner

1. Plug an OBD2 scanner into the port under the dashboard and read all stored codes and the freeze-frame data (the conditions when the code set).
2. Scan for other throttle and pedal codes; they help narrow it down.
3. Key on, engine off: watch the throttle position reading in live data. A reading near the top of its range with the throttle closed matches this code.
4. With the key off, unplug the throttle body or sensor and inspect the connector for corrosion, water or pushed-back pins, and the wiring for damage. Keep fingers out of the throttle bore whenever the key is on, since an electronic throttle plate can move on its own.
5. Many vehicles need a throttle relearn (idle relearn) after replacing the throttle body or sensor; check the procedure for your vehicle.
6. After a repair, clear the code and drive normally for a few days to confirm it doesn't come back.

A basic code reader shows the code; scanners with live data let you watch sensor readings, which is what you need for most of the checks above. See OBD2 scanners under $100.

Questions

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