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

What does P0123 mean?

The throttle and pedal position sensors tell the ECM how far the throttle is open and how much power you ask for. A voltage that stays too high points to a short or a sensor fault rather than a real full throttle request.

As with P0122, the ECM may limit throttle opening as a fail safe, so the car may drive slowly until the fault is repaired.

Common symptoms

• Check engine light on
• Hesitation on acceleration
• Hard starting in some cases
• Reduced power or limited throttle response
• Higher than normal idle in some cases

Common causes

The causes below are the ones commonly seen with P0123. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

• A faulty throttle position sensor
• Shorted, chafed or corroded wiring or connectors in the sensor circuit
• A dirty or carbon filled throttle body on some vehicles (listed by RepairPal)

What to check with a scanner

• In Live data, check throttle position with your foot off the pedal. A high reading at rest points to the circuit or sensor.
• Slowly press the pedal and watch for jumps or spikes.
• Inspect connectors and wiring for damage, especially near hot or moving parts.
• Clear the code and see whether it returns.

How to read and clear P0123 with OBD Master Pro

1. Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
2. Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
3. Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
4. Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P0123 is listed and note any other codes, since they often explain the cause.
5. Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
6. Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P0123 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P0123.

When to see a mechanic

Get professional help if any of these apply:

• The car goes into reduced power mode
• The idle is high or the engine surges
• Wiring needs testing for shorts

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

Related trouble codes

See all OBD2 trouble code guides

Related guides

Check engine light on: what to do · How to read an OBD2 code (P, B, C, U) · Stored, pending and permanent codes and freeze frame · OBD2 readiness monitors explained · OBD2 glossary · OBD2 by car brand