P0120
TPS Circuit Malfunction
medium
i Description
The Throttle Position Sensor (TPS) circuit has a malfunction. The TPS tells the ECU how far the throttle valve is open, which is critical for fuel delivery, shift timing, and traction control.
? Common Causes
- Worn TPS (internal resistance element degraded)
- Loose or corroded TPS connector
- Damaged wiring
- Throttle body fault
- ECU fault (rare)
! Symptoms
- Check engine light
- Erratic or surging idle
- Hesitation on acceleration
- Poor throttle response
- Transmission shifting issues
# Diagnostic Steps
- Backprobe TPS signal wire and sweep throttle slowly — voltage should rise smoothly
- Check for dead spots or dropouts in signal
- Inspect connector for corrosion
- Test reference voltage (should be ~5V)
- Replace TPS if signal is erratic
⚙ Typical Fix
Replace the throttle position sensor. Some vehicles require throttle body cleaning or relearning.
Parts Needed
Throttle position sensor
Estimated Cost
$80-$300
↔ Related Codes
Q Frequently Asked Questions
The car may be difficult to drive — expect erratic idle and poor throttle response. Some vehicles enter limp mode. Get it fixed soon.
Yes. The TPS is usually on the side of the throttle body, held by two screws. Replacement is straightforward on most vehicles.
TPS sensor: $30-$150. Mechanic labour: $50-$150.
☞ Learn More
- What is OBD-II? — Complete guide to your car's diagnostic system
- How to Read DTC Codes — Step-by-step with a Bluetooth scanner
- OBD-II Scanner Buying Guide — Find the best scanner for your car