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P0587Cruise Control Vent Control Circuit Low

The cruise control vent solenoid circuit is reading lower voltage than expected, usually from a short to ground, and the module has disabled cruise control.

Definition

The control module drives the vent solenoid in the cruise servo to bleed off vacuum and reduce throttle pull, monitoring the circuit voltage against its commands. P0587 sets when the vent control circuit remains low when it should be high, which typically means a short to ground in the wiring or a shorted solenoid winding. A grounded vent circuit would hold the vent open or closed regardless of command, so the module shuts the cruise system down as soon as the fault is seen. The only symptom is inoperative cruise control; engine performance is unaffected and the MIL usually does not illuminate.

Common causes

  • Vent control wire chafed through to ground in the servo harness
  • Shorted vent solenoid winding with below-specification resistance
  • Moisture or corrosion inside the servo connector creating a path to ground
  • Harness pinched during prior repairs near the servo mounting bracket
  • Failed driver in the cruise or engine control module

Common misdiagnoses

  • Servo assembly replaced when the harness short is the actual fault
  • Control module condemned before the circuit is checked for a ground short
  • Brake switch replaced for an actuator-circuit code
  • Vacuum leak diagnosis performed for a purely electrical fault

Troubleshooting steps

  1. 1.Measure vent solenoid resistance

    Compare the measured value against specification; a few ohms instead of the typical 20-60 ohm range indicates a shorted winding.

  2. 2.Check the control wire for a ground short

    With both ends disconnected, measure resistance from the vent control wire to chassis ground and expect OL; any continuity confirms a harness short.

  3. 3.Wiggle-test the harness

    Watch the circuit status on a meter or scan tool while flexing the servo harness to catch an intermittent chafe point.

  4. 4.Inspect the connector seal

    Open the servo connector and look for water staining or corrosion that could bridge the vent terminal to ground.

  5. 5.Verify operation after repair

    Command the vent solenoid with the scan tool and confirm the circuit toggles cleanly, then road-test cruise engagement and cancellation.

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