P0120
High SeverityThrottle Position Sensor A Circuit
Fuel System
P0120 — Instant Answer
Throttle Position Sensor A Circuit
Severity: HIGH SEVERITY
Meaning: General fault in the TPS circuit. The TPS tells the ECM how far the throttle is open.
Safe to drive? NO if CEL is flashing. YES with caution if solid, but repair this week.
Estimated repair cost: $20 - $150
Most common causes:
- 1. Faulty TPS (35-45% of cases)
- 2. Corroded TPS connector (10-25% of cases)
- 3. Wiring issue (10-25% of cases)
- 4. Worn throttle body (10-25% of cases)
Symptoms
- ⚠️Erratic idle
- ⚠️Hesitation on acceleration
- ⚠️Surging
- ⚠️Reduced power mode
Common Causes
How to Diagnose P0120
- 1Check TPS connector for corrosion
- 2Sweep TPS with scan tool — look for dropouts
- 3Measure TPS voltage at closed and WOT
- 4Replace TPS if erratic
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The TPS reading does not match expected values based on MAP, RPM, and other inputs. Erratic readings indicate a worn TPS.
TPS voltage is below minimum threshold. The ECM cannot determine throttle position accurately.
TPS voltage is above maximum expected. ECM sees the throttle as more open than it actually is.
Frequently Asked Questions
- Can a dirty throttle body cause P0120?
- Yes — carbon buildup can prevent the throttle from closing fully, confusing the TPS. Clean the throttle body first.
- What is limp mode?
- When the ECM cannot trust the TPS, it limits power to protect the engine. This is called limp mode or reduced power mode.
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Author & Review
Written by AllOEMManuals Editorial Team. Reviewed by ASE-certified technicians and updated with factory-reference checks for fitment-sensitive steps.
This guide was drafted with AI assistance and reviewed for accuracy by a human editor.
Last updated: 2026-05-07