P0578 Cruise Control Multi-Function Input A Circuit Stuck

P0578 points to Cruise Control Multi-Function Input A circuit stuck. The controller sees input A held in one state longer than expected.

Code details

Generic OBD-II · P0

System: Speed / Idle
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace cruise output components when the fault is a stuck input command.

Symptoms of P0578

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 P0578

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 multi-function input A data, individual switch states, brake input, vehicle speed, cruise enable status, and freeze-frame data.
Inspect stuck steering wheel switch contacts, spilled liquid contamination, clockspring wiring, resistor ladder faults, and connector corrosion.
Operate all input A switch positions and confirm the signal returns to neutral after each command.

Related OBD-II codes

These nearby speed / idle entries can help compare wording and pin down the fault area.