What Does P0596 Mean?
The cruise control servo control circuit is reporting a high voltage condition. The PCM detects elevated voltage on the servo control line, suggesting an open in the ground path, a disconnected servo, or a short to a voltage source. The cruise control system will be disabled because the PCM cannot properly modulate the servo.
Common Causes
30%
Open ground circuit for the cruise control servo
25%
Disconnected or open cruise control servo connector
20%
Cruise control servo motor with open winding
15%
Short to battery voltage in the servo control wire
10%
PCM or cruise module output driver open fault
Diagnostic Steps
1
Verify the cruise control servo connector is fully plugged in and the locking tab is engaged — vibration can cause connectors on the firewall to work loose.
2
Measure voltage at the servo connector with the cruise commanded on — the control pin should show a modulated ground signal from the PCM; constant high voltage indicates an open ground path.
3
Check the servo motor resistance — 30-60 ohms is typical; OL (open) confirms a burned-out motor winding.
4
Inspect the ground wire from the servo to the vehicle body or engine ground point for corrosion, loose mounting, or a broken wire.
5
If the servo and ground test good, check for battery voltage on the control wire with the servo disconnected — the presence of B+ indicates a short to voltage in the harness.
Estimated Repair Cost
$120 - $550
Parts + labor, varies by vehicle and location
The cruise control servo control circuit is reporting a high voltage condition. The PCM detects elevated voltage on the servo control line, suggesting an open in the ground path, a disconnected servo, or a short to a voltage source. The cruise control system will be disabled because the PCM cannot p...
The most common cause of P0596 (Cruise Control Servo Control Circuit High) is: Open ground circuit for the cruise control servo
Typical repair costs for P0596 range from $120 to $550, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. An open or high-voltage servo circuit means the cruise cannot apply throttle, so there is no risk of unintended acceleration. The cruise control system will simply not function until repaired. Normal driving is completely unaffected.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0596 to identify the root cause.
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Quick Info
Category
Powertrain
System
Cruise Control / Speed Control
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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