Symptoms of P0593
- 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 P0593
- 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 input B voltage, switch states, reference voltage, ground path, input A correlation, brake switch data, and freeze-frame conditions.
- Inspect for short-to-voltage faults, open grounds, damaged clockspring wiring, stuck switch contacts, liquid intrusion, and connector corrosion.
- Operate each input B function while watching live data to see whether the signal is stuck high or only high for one switch.
Related OBD-II codes
These nearby speed / idle entries can help compare wording and pin down the fault area.