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P0595Cruise Control Servo Control Circuit Low

The cruise control servo control circuit is reading a lower voltage than expected, usually because of a short to ground, and the module has shut down the cruise system.

Definition

The module monitors feedback on the servo control circuit while driving the cruise actuator and expects the voltage to follow its commands. P0595 sets when the circuit remains low when commanded high, indicating a short to ground in the harness or a shorted winding inside the servo. Since an uncontrolled grounded driver circuit could keep the actuator energized, the module disables cruise, commonly by opening the cruise enable relay, the moment the fault is detected. The vehicle drives normally otherwise, and the MIL usually stays off for this fault.

Common causes

  • Servo control wire chafed to ground along the engine harness
  • Shorted motor winding or clutch coil inside the servo actuator
  • Water intrusion and corrosion in the servo connector bridging to ground
  • Harness pinched at a bracket or during prior engine service
  • Failed low-side driver in the cruise or engine control module

Common misdiagnoses

  • Servo replaced when the harness chafe is the real short
  • Control module condemned before isolating the circuit
  • Cruise fuse or relay replaced repeatedly without finding the short
  • Speed sensor replaced because cruise drops out

Troubleshooting steps

  1. 1.Measure actuator winding resistance

    Compare each servo circuit's resistance to specification; a near-zero reading indicates a shorted winding dragging the control circuit low.

  2. 2.Isolate the harness

    With the servo and module both disconnected, measure the control wire to chassis ground; any continuity confirms a harness short to trace out.

  3. 3.Inspect known chafe points

    Check where the servo harness crosses brackets, the accessory drive area, and any sections disturbed in previous repairs.

  4. 4.Check the connector for moisture

    Open the servo connector and look for water staining or green corrosion that can leak current to ground.

  5. 5.Confirm command response

    After repair, command the servo with the scan tool and verify the circuit voltage toggles with the command before clearing the code and road-testing.

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