P0579 Cruise Control Multi-Function Input A Circuit Range/Performance

P0579 indicates a range or performance issue in Cruise Control Multi-Function Input A circuit. The input voltage exists but does not match expected switch positions.

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 the controller until switch resistance, clockspring wiring, and reference voltage are checked.

Symptoms of P0579

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 P0579

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 input A voltage or data values with each switch position, brake status, vehicle speed, and freeze-frame operating conditions.
Inspect resistor ladder values, switch contact resistance, clockspring wiring, connector tension, corrosion, and module reference voltage.
Operate each function in input A and verify the scan-tool value lands in the expected range without drifting.

Related OBD-II codes

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