Symptoms of P0555
- Unstable, high, or low idle, or stalling.
- Erratic speedometer, cruise-control, or shift behaviour.
- Check-engine light with a hesitation or surge.
Common causes of P0555
- A dirty throttle body, idle-control valve, or throttle-position sensor.
- A failing vehicle-speed or wheel-speed sensor, or its wiring.
- Vacuum leaks or a related sensor forcing the idle/speed strategy.
Useful checks before replacing parts
- Compare brake booster pressure data, manifold vacuum, brake pedal input, engine load, idle behavior, freeze-frame data, and brake assist warnings.
- Inspect sensor reference voltage, ground, signal wiring, vacuum hose condition, booster check valve, connector corrosion, and vacuum pump operation where equipped.
- Apply and release the brake pedal while watching sensor response to verify pressure changes are smooth and believable.
Related OBD-II codes
These nearby speed / idle entries can help compare wording and pin down the fault area.