P0121 — Throttle/Pedal Position Sensor A Range/Performance
Moderate severityWhat it means
P0121 is stored when the engine control unit sees a fault involving throttle/pedal position sensor A. Throttle/pedal position sensor A tells the control unit how far the throttle or accelerator pedal is opened; it is central to drive-by-wire throttle control. A “range/performance” fault means the value is present but implausible — it does not agree with other sensors or expected conditions.
Common symptoms
- Readings that drift or disagree with related sensors
- Hesitation, surging or poor throttle response
- Reduced power or limp mode
- Unstable idle
Likely causes
- Drifting, contaminated or aged sensor
- A mechanical issue skewing the reading
- Worn throttle position sensor or throttle body
- Connector or wiring fault
What to check first
- Cross-check the reading against related sensors in live data on a cold start
- Watch the throttle/pedal percentage sweep smoothly from 0 to 100% in live data
- Inspect the connector and check whether a throttle relearn is needed
Can you keep driving?
Drive-by-wire faults often trigger reduced-power mode; diagnose promptly because throttle response can be unpredictable.
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