OBD-II Code P0594 — What It Means & How to Fix It

What Does This Error Mean?

P0594 means there is a problem with the cruise control servo control circuit. The servo is the mechanical actuator that physically moves the throttle to hold your set speed. The PCM controls the servo with an electrical signal — and when that circuit has a fault, P0594 is triggered. Cruise control will not function. Your normal throttle pedal and engine operation are not affected.

Affected Models

All vehicles 1996+
Common in older vehicles with vacuum-operated cruise control servos
Common in GM, Ford, and Chrysler vehicles pre-2010
Less common on newer vehicles with electronic throttle control (drive-by-wire)
Common in any vehicle using a dedicated cruise control servo unit

Common Causes

Failed cruise control servo unit — motor or solenoid inside the servo has worn out
Open or short in the wiring between the PCM and the cruise control servo
Corroded or damaged servo connector causing an intermittent fault
Blown fuse for the cruise control servo circuit
PCM output driver failure — rare, but the PCM can fail to drive the servo properly

How to Fix It

Start by checking the cruise control fuse. Look in your owner's manual for the fuse box location and the specific cruise control fuse. Replace any blown fuse with one of the correct amperage rating.

A repeatedly blown fuse points to a short circuit in the servo or wiring — do not keep replacing fuses without finding the root cause.
Locate the cruise control servo unit. On older vehicles it is typically a canister mounted in the engine bay with a cable running to the throttle linkage. Inspect the cable for fraying, kinking, or binding that could strain the servo.

If the throttle cable from the servo is binding, the servo motor will overload and can trigger circuit faults.
Inspect the electrical connector at the servo. Check for corrosion, damaged pins, or wires that have pulled out of the connector housing. Clean any corrosion with electrical contact cleaner.

Servo connectors are often exposed to heat and engine bay moisture — corrosion here is a very common cause.
With the connector plugged in, use a multimeter or test light to check for power and ground at the servo while commanding it to activate. If power and ground are present but the servo does not respond, the servo is faulty.

You can use a scan tool bidirectional control (if available) to activate the servo for testing.
Replace the servo if it fails the electrical test. Clear the code after installation and test cruise control at highway speed to confirm the fix.

After replacing a cable-actuated servo, check and adjust the throttle cable freeplay if required by your vehicle's service manual.

When to Call a Professional

If the fuse and wiring check out, servo replacement is usually a straightforward repair. A shop can confirm the servo is faulty by testing the circuit voltage at the servo connector. Servo replacement typically costs $80 to $200 in parts, plus 1 to 2 hours of labor. If the PCM driver circuit is suspect, professional diagnosis is recommended before replacing the module.

Frequently Asked Questions

What does a cruise control servo actually do?

The servo is the part that physically opens the throttle to maintain your set speed. When you engage cruise control and set a speed, the PCM sends signals to the servo, which pulls the throttle cable (or actuates a motor) to hold the throttle at the right opening. It is basically a robot hand on the throttle.

My car is newer — do I still have a cruise control servo?

Newer vehicles with electronic throttle control (no physical throttle cable) do not use a traditional servo. On these cars, the PCM directly controls the electronic throttle actuator to maintain cruise speed. P0594 on a newer vehicle may point to a different circuit — check your vehicle's specific documentation.

Can I drive with P0594?

Yes, driving is safe. P0594 only affects cruise control. Your accelerator pedal and engine operate normally. Just do not attempt to engage cruise control while this code is active.