Throttle/Pedal Position Sensor A Circuit High Input
The P0123 code means the vehicle's onboard diagnostic system has detected: Throttle/Pedal Position Sensor A Circuit High Input. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- medium
- Estimated cost
- $30-$120
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Common Symptoms
- Check Engine Light on
- High idle speed
- Reduced power / failsafe (limp) throttle limiting
- Engine limp mode
- Throttle sluggish
Probable Causes (Ranked by Likelihood)
- TPS signal voltage above maximum threshold Very High
- Short to 5V reference or 12V in signal wire High
- Failed TPS with stuck-high output High
- Damaged or corroded connector or signal wiring (corrosion or chafing) Moderate
- PCM input circuit fault Low
Step-by-Step Diagnostic Procedure
-
Check TPS signal voltage at idle. Above 4.8V at rest indicates a high signal fault.
-
Disconnect the TPS connector and back-probe the signal wire. Because the PCM pulls this input up, an unplugged signal wire normally floats high (near 5V). If the voltage drops to near 0V when the sensor is disconnected, the high reading was coming from the sensor (replace the TPS); if it stays high with the sensor unplugged, suspect a short to the 5V reference or battery voltage in the harness.
-
Inspect wiring for contact with 5V reference or other voltage sources.
-
Replace TPS if signal voltage does not drop when sensor is disconnected.
Common Fixes by Vehicle
What techs usually find when diagnosing P0123 on specific vehicles — tap your vehicle for the fix and the exact part:
1999-2013 Chevrolet/GMC trucks & SUVs easy DIY
Throttle position sensor A high input means the TPS signal read out of range. On cable throttle bodies the sensor alone can be replaced; on electronic (drive-by-wire) bodies the sensor is integral and you replace the throttle body. Check the connector and wiring for corrosion first — a backed-out pin mimics a bad sensor.
Labor: 30-45 minFrequently Asked Questions
Is a high TPS reading dangerous?
It can be. A stuck-high TPS signal tells the ECU the throttle is wide open at all times. The ECU may richly fuel the engine or enter limp mode. Have this diagnosed promptly.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P0123 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
See All Codes & Fixes for Your Vehicle
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