P0121
High SeverityThrottle Position Sensor A Range/Performance
Fuel System
P0121 — Instant Answer
Throttle Position Sensor A Range/Performance
Severity: HIGH SEVERITY
Meaning: The TPS reading does not match expected values based on MAP, RPM, and other inputs. Erratic readings indicate a worn TPS.
Safe to drive? NO if CEL is flashing. YES with caution if solid, but repair this week.
Estimated repair cost: $20 - $100
Most common causes:
- 1. Worn TPS with dead spots (35-45% of cases)
- 2. Throttle body carbon buildup (10-25% of cases)
- 3. Loose TPS connector (10-25% of cases)
- 4. Damaged throttle linkage (5-10% of cases)
Symptoms
- ⚠️Intermittent power loss
- ⚠️Rough acceleration
- ⚠️Surging at cruise speed
- ⚠️Reduced power mode
Common Causes
How to Diagnose P0121
- 1Watch TPS voltage on scan tool while slowly opening throttle — look for jumps or dropouts
- 2Clean throttle body
- 3Check TPS mounting and connector
- 4Replace TPS if readings are erratic
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General fault in the TPS circuit. The TPS tells the ECM how far the throttle is open.
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
- How do I test a TPS?
- Using a scan tool, slowly open the throttle from closed to wide open. Voltage should rise smoothly from ~0.5V to ~4.5V with no jumps or drops.
- Can I just clean the throttle body?
- Sometimes cleaning fixes P0121 if carbon is preventing smooth throttle movement. Try cleaning first before replacing the TPS.
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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