Cruise Control Servo Control Circuit/Open
The P0594 code indicates a problem in the cruise control servo control circuit, which is responsible for adjusting the throttle position to maintain set speed. The Powertrain Control Module (PCM) detects an open or short circuit in the servo control wiring or a malfunctioning servo motor. This can prevent the cruise control from engaging or cause it to disengage unexpectedly.
1. Most Common Causes
- Open or short circuit in the cruise control servo control wiring
- Faulty cruise control servo motor
- Corroded or damaged electrical connectors
- Failed PCM (rare)
2. Symptoms You Will Notice
- Cruise control inoperative or intermittent operation
- Cruise control light on dash flashing or staying on
- Engine Check Light illuminated
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0594 and check for other codes.
Step 2: Visually inspect the cruise control servo wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the servo control circuit for continuity and shorts using a multimeter.
Step 4: Check the servo motor resistance and compare to manufacturer specs.
Step 5: If wiring and servo are good, test the PCM output signals to the servo.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
Yes, the vehicle is safe to drive, but cruise control will not function. The code does not affect normal driving or engine performance.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, depending on whether the issue is a wiring repair (cheaper) or servo replacement (more expensive).
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.