Broken or disconnected wire in the cruise control servo control circuit; Corroded or loose electrical connector at the cruise control servo; Failed cruise control servo motor or actuator; Open winding inside the servo motor; Faulty brake pedal position switch (often integrated with the cruise control circuit); Damaged or shorted wiring harness due to chafing or rodent damage; Internal ECM driver circuit failure (rare but possible)

DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P0594

P0594Cruise Control Servo Control Circuit/Open

Q: What does code P0594 mean?

Cruise Control Servo Control Circuit/Open. P0594 indicates that the engine control module (ECM) has detected an open circuit in the cruise control servo control circuit, meaning the electrical path to the servo is broken or has excessive resistance. The ECM commands the servo to adjust throttle position for cruise control, but the circuit's feedback does not match the expected voltage or current, setting this code.

P0594 indicates that the engine control module (ECM) has detected an open circuit in the cruise control servo control circuit, meaning the electrical path to the servo is broken or has excessive resistance. The ECM commands the servo to adjust throttle position for cruise control, but the circuit's feedback does not match the expected voltage or current, setting this code.

SystemPowertrain

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

Cruise control system fails to engage or disengages unexpectedly while driving
Cruise control indicator light on the dashboard may flash or stay off when trying to activate
No other drivability symptoms; the vehicle otherwise runs and drives normally
Possible stored code without any noticeable performance change
In some vehicles, a chime or message may appear indicating cruise control is unavailable

Common causes, most likely first

Broken or disconnected wire in the cruise control servo control circuit
Corroded or loose electrical connector at the cruise control servo
Failed cruise control servo motor or actuator
Open winding inside the servo motor
Faulty brake pedal position switch (often integrated with the cruise control circuit)
Damaged or shorted wiring harness due to chafing or rodent damage
Internal ECM driver circuit failure (rare but possible)

How to diagnose and fix it

Inspect the cruise control servo connector and wiring for obvious damage, corrosion, or loose pins
Check the cruise control fuse and relay, and replace if blown or faulty
Disconnect the servo and measure resistance across the servo motor terminals; compare to manufacturer's specification
Perform a voltage drop test on the control circuit while commanding the servo on with a scan tool
Check the brake pedal position switch for proper operation and continuity
Repair or replace any damaged wiring or connectors, then clear the code and verify the repair
If all external circuits test good, suspect the ECM and perform further diagnostics before replacement

Cruise Control Servo Circuit Pitfalls

A common misdiagnosis is replacing the cruise control servo when the real problem is a faulty brake pedal switch, which can interrupt the circuit and set P0594.
The code can be set by a simple blown fuse that also powers other systems, so always check fuses before condemning the servo.
On some vehicles, the cruise control servo is integrated into the throttle body, and a dirty throttle body can cause intermittent servo operation and set this code.
An open circuit can be caused by a chafed wire hidden inside a loom, often near the firewall or where the harness flexes with engine movement.
P0594 does not always mean the servo is bad; the ECM may set it if it detects an unexpected voltage on the control circuit due to a poor ground connection.

Can I keep driving with P0594?

The vehicle remains safe to drive because cruise control is a convenience feature and its failure does not affect basic operation. Avoid using cruise control until the fault is repaired, and be aware that some vehicles may disable other driver-assist features that rely on the same circuit.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.