P0591 Cruise Control Multi-Function Input B Circuit Range/Performance

P0591 indicates a range or performance issue in Cruise Control Multi-Function Input B circuit. The input B value is present but not valid for the commanded switch position.

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 and clockspring wiring are verified.

Symptoms of P0591

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 P0591

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

Related OBD-II codes

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