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.

P0121

High Severity

Fuel System

The TPS reading does not match expected values based on MAP, RPM, and other inputs. Erratic readings indicate a worn TPS.

Common Fix

Replace TPS

Estimated Cost (DIY)

$20 - $100

Worn TPS with dead spotslikely

Throttle body carbon builduppossible

Loose TPS connectorpossible

Damaged throttle linkageunlikely

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

Need to read or clear this code?

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.

Need a diagnosis for your specific vehicle?

100% Free — No signup required