Throttle/Pedal Position Sensor A Circuit Malfunction
What does P0120 mean?
The P0120 code means the vehicle's onboard diagnostic system has detected: Throttle/Pedal Position Sensor A Circuit Malfunction. This is a serious severity code.
Common Symptoms
- Check Engine Light on
- Hesitation or stumble on acceleration
- Erratic idle speed
- Engine may enter limp mode
- Throttle unresponsive
Probable Causes (Ranked by Likelihood)
- Faulty throttle position sensor (TPS) Very High
- Wiring damage or corrosion at TPS connector High
- Throttle body carbon buildup affecting TPS sweep Moderate
- PCM throttle input circuit fault Low
Step-by-Step Diagnostic Procedure
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Monitor TPS voltage with a scan tool during slow throttle opening from idle to WOT. It should sweep smoothly from about 0.5V to 4.5V.
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Any dropout, spike, or dead zone in the sweep indicates a failing TPS.
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Check connector for corrosion and loose pins.
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Clean throttle body if carbon is restricting plate movement.
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Measure TPS voltage at rest: should be 0.45-0.55V on most applications.
Frequently Asked Questions
What is a TPS and what does it control?
The throttle position sensor measures the angle of the throttle plate. The ECU uses this to calculate how much fuel to inject, adjust ignition timing, and control transmission shift points.
Can I adjust a TPS to fix P0120?
On older cable-throttle engines with adjustable sensors, sometimes. On modern drive-by-wire systems, the TPS is sealed inside the throttle body and cannot be adjusted.