Cruise Control Servo Control Circuit/Open
The P0594 code indicates a problem in the cruise control servo control circuit, which is responsible for controlling the throttle position to maintain set speed. The Powertrain Control Module (PCM) has detected 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.
01. Most Common Causes
- Faulty cruise control servo motor
- Open or shorted wiring in the servo control circuit
- Corroded or loose electrical connectors
- Failed PCM (rare)
02. Symptoms You Will Notice
- Cruise control inoperative
- Cruise control light on dash flashing or staying on
- Check Engine Light illuminated
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all stored codes and freeze frame data.
Step 2: Visually inspect the cruise control servo wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the servo motor resistance and voltage supply using a multimeter, comparing to manufacturer specifications.
Step 4: If wiring and servo are okay, check for PCM software updates or replace PCM if necessary.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
Yes, it is generally safe to drive, but cruise control will not function. The vehicle's normal braking and throttle operation are unaffected.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and repair, depending on whether it's a wiring fix or servo replacement.