Symptoms of P0559
- 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 P0559
- 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
- Review brake assist complaints, freeze-frame data, pedal application history, vacuum pump operation where equipped, and whether the fault follows vibration or moisture.
- Inspect connector tension, sensor wiring, vacuum hose movement, check valve condition, reference voltage, ground quality, and harness flex points.
- Graph booster pressure during repeated brake applications and harness movement to catch brief interruptions.
Related OBD-II codes
These nearby speed / idle entries can help compare wording and pin down the fault area.