P0594 Cruise Control Servo Control Circuit/Open

P0594 indicates an open cruise control servo control circuit. The controller does not see expected continuity or current through the cruise servo control path.

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 switches when the fault points to an open servo control circuit.

Symptoms of P0594

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 P0594

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

Check servo command, supply voltage, control continuity, actuator resistance, cruise enable status, vehicle speed, and freeze-frame data.
Inspect servo connector, wiring opens, fuse feeds, grounds, vacuum or cable actuator condition, linkage movement, and module output pins.
Command the servo according to service procedures and verify both circuit response and actuator movement.

Related OBD-II codes

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