P0587 LOW VOLTAGE DETECTED AT THE SPEED CONTROL VENT DRIVER

When Monitored and Set Condition:

When Monitored: While driving and the Speed control is set.
Set Condition: This code will set if the voltage detected on the Speed Control Vent circuit at the ECM is
different than the expected voltage for 3 seconds.

POSSIBLE CAUSES

• P0595 OR P0596 PRESENT
• SPEED CONTROL SERVO ASSEMBLY
• (V35) SPEED CONTROL VENT CIRCUIT OPEN
• (V35) SPEED CONTROL VENT CIRCUIT SHORTED TO GROUND
• (V35) SPEED CONTROL VENT CIRCUIT SHORTED TO OTHER CIRCUITS
• ECM
• INTERMITTENT CONDITION
• SPEED CONTROL SERVO

DIAGNOSTIC PROCEDURE

1. With the DRBIII®, read DTCs. Is the P0595 or P0596 set?
   Yes --> Repair the other DTCs first.
   No --> Go To 2
2. Turn the ignition off. Disconnect the Speed control servo harness connector.
   NOTE: Check connectors - Clean/repair as necessary.
   Ignition on, engine not running. With the DRBIII®, actuate the Speed Control Vent Solenoid. Using a 12-volt test light connected to battery positive, check the Speed Control Vent Solenoid Output circuit in the Speed Control Assembly harness connector.
   NOTE: The test light must illuminate brightly.
   Compare the brightness to that of a direct connection to the battery. Does the test light cycle on and off and illuminate brightly?
   Yes --> Replace the speed control servo assembly.
   No --> Go To 3
3. Turn the ignition off. Disconnect the ECM harness connector(s).
   NOTE: Check connectors - Clean/repair as necessary.
   Measure the resistance of the Speed Control vent circuit between the Cruise Control Assembly harness connector and the ECM harness connector. Is the resistance below 5.0 ohms?
   Yes --> Go To 4
   No --> Repair the (V35) Speed Control vent circuit for an open.
4. Measure the resistance between ground and the Speed Control vent circuit in the ECM harness connector. Is the resistance below 5.0 ohms?
   Yes --> Repair the (V35) Speed Control vent circuit for a short to ground.
   No --> Go To 5
5. Measure the resistance between the Speed Control Vacuum circuit and all other circuits in the ECM connectors. is the resistance less than 10 ohms?
   Yes --> Repair the (V35) Speed Control vent circuit shorted to other circuit.
   No --> Go To 6
6. Reconnect the ECM harness connectors. Ignition on, engine not running. With the DRBIII®, actuate the Speed Control Vent Solenoid. Using a 12-volt test light connected to battery positive, check the Speed Control Vent Solenoid Output circuit in the Speed Control Assembly harness connector.
   NOTE: The test light must illuminate brightly.
   Compare the brightness to that of a direct connection to the battery. Does the test light cycle on and off and illuminate brightly?
   Yes --> Go To 7
   No --> Replace and program the ECM in accordance with the Service Information.
7. Refer to the SYMPTOM: INTERMITTENT CONDITION Symptom (Diagnostic Procedure). Where any problems found?
   Yes --> Refer to the SYMPTOM: INTERMITTENT CONDITION.
   No --> Replace the Speed control servo.