P0721 — Output Speed Sensor Circuit Range/Performance
Moderate severityWhat it means
P0721 is stored when the engine control unit sees a fault involving the output speed sensor circuit. The output speed sensor measures the transmission's output shaft speed (vehicle speed); the control unit uses it for shift timing and the speedometer. 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
- Speedometer dead or erratic
- Harsh or wrong-timed shifts
- Limp mode in some cases
Likely causes
- Drifting, contaminated or aged sensor
- A mechanical issue skewing the reading
- Faulty output speed sensor
- Wiring/connector fault at the transmission
What to check first
- Cross-check the reading against related sensors in live data on a cold start
- Compare output speed in live data with actual/GPS speed
- Inspect the sensor connector and wiring
Can you keep driving?
Drivable with care, but shifting and the speedometer may misbehave; diagnose soon.
Frequently asked questions
What is the most common cause of P0721?
The most likely cause is: Drifting, contaminated or aged sensor. Several other faults can set P0721 as well, so confirm the real cause with live data and the checks above before replacing any parts.
Can I just clear P0721 and keep driving?
Clearing P0721 with an OBD2 scanner turns the warning light off, but if the underlying fault has not been repaired the code will usually come back within a few drive cycles. Fix the cause first, then clear the code to confirm the repair worked.
How serious is P0721?
P0721 is a moderate-severity code. The car is often still drivable, but have it diagnosed soon — the underlying problem can get worse and it may fail an emissions test.
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