P0594: Cruise Control Servo Control Circuit Open

What it means

The servo motor that drives the cruise control throttle actuator has an open control circuit. The ECU cannot drive the servo - cruise control is unavailable.

At a glance

• Usually lights the check-engine light

How it works

The cruise-control servo is an actuator that moves the throttle to maintain the set speed. P0594 sets when the control module detects an open in the servo control circuit and cannot drive the actuator, so cruise control may be unavailable or disengage.

Common causes

Most likely first.

1. Open in motor or harness
2. Pin pushed back out of connector body
3. Cracked solder joint inside the module or sensor

Symptoms

• Cruise control unavailable
• Cruise control may disengage
• Check-engine light

How to diagnose it

1. Use a scan tool to confirm P0594 and review freeze-frame data and cruise-servo commands to establish when the open was detected.
2. Inspect the servo connector and harness for a loose plug, broken wire, corrosion, or a pushed-back terminal.
3. Check circuit continuity through the servo control wiring and motor using the wiring diagram to locate the open.
4. Wiggle the harness and connectors while monitoring the circuit or repeating the appropriate scan-tool test to find an intermittent open.
5. If the external circuit is intact, test the servo and control module according to the manufacturer's specification.

Common fixes

• Reconnect a loose servo plug and secure the harness.
• Repair a broken or open wire in the servo control circuit.
• Replace damaged connector terminals or restore a pushed-back pin.
• Replace a failed servo or repair the module only after the circuit tests confirm the fault.

Can I keep driving?

Driving is generally possible if normal throttle and braking operation are unaffected, but cruise control may not work or may disengage. Do not rely on it to maintain speed.