P0594
P0594-SPEED CONTROL SERVO POWER RELAY CIRCUITP0594-Speed Control Servo Power Relay Circuit:
WHEN MONITORED
With the ignition key on. The speed control switched on.
SET CONDITION
The speed control power supply circuit is either open or shorted to ground for more than 2.6 seconds. One Trip Fault. Three good trips to turn off the MIL.
POSSIBLE CAUSES
- (V32) S/C supply circuit open
- (V32) S/C supply circuit shorted to ground
- (V30) S/C brake switch output circuit open
- (V30) S/C brake switch output circuit shorted to ground
- Stop lamp switch
- PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test
1. ACTIVE DTC
NOTE: If this code is setting on a vehicle that doesn't have a S/C Servo, flash the correct code into the PCM or the wrong PCM may have previously been installed.
Ignition on, engine not running.
With a scan tool, read DTCs.
Q: Is the DTC active at this time?
YES: Go To 2
NO: Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Component Tests and General Diagnostics
Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
2. (V32) S/C SUPPLY CIRCUIT
Turn the ignition off.
Disconnect the Stop Lamp Switch harness connector.
Ignition on, engine not running. (It may be necessary to start the engine.)
Using a 12-volt test light connected to ground, probe the (V32) S/C Supply circuit in the Switch harness connector while holding the Cruise Switch in the ON position.
Q: Does the test light illuminate brightly?
YES: Go To 3
NO: Go To 7
3. STOP LAMP SWITCH
Disconnect and remove the Stop Lamp Switch.
Measure the resistance across the (V32) S/C Supply circuit terminal and the (V30) S/C Brake Switch Output circuit terminal in the Stop Lamp Switch.
Push the Plunger of the Switch in and let it out.
Q: Does the resistance change from below 5.0 ohms to an open circuit?
YES: Go To 4
NO: Replace the Stop Lamp Switch. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
4. (V30) S/C BRAKE SWITCH OUTPUT
Turn the ignition off.
Connect the Stop Lamp Switch harness connector and install the Switch.
Disconnect the Speed Control Servo harness connector.
Ignition on, engine not running.
NOTE: It is necessary to PRESS and HOLD the Speed Control Switch in the ON position while checking for voltage.
Using a 12-volt test light connected to ground, probe the (V30) S/C Brake Switch Output circuit in the Servo Harness connector.
Q: Does the test light illuminate brightly?
YES: Replace the S/C Servo. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 5
5. (V30) S/C BRAKE SWITCH OUTPUT CIRCUIT OPEN
Turn the ignition off.
Disconnect the Brake Lamp Switch harness connector.
Measure the resistance of the (V30) S/C Brake Switch Output circuit from the Stop Lamp Switch harness connector to the S/C Servo harness connector.
Q: Is the resistance below 5.0 ohms?
YES: Repair the excessive resistance in the (V30) S/C Brake Switch Output circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 6
6. (V30) S/C BRAKE SWITCH OUTPUT CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (V30) S/C Brake Switch Output circuit in the Speed Control Servo harness connector.
Q: Is the resistance below 100 ohms?
YES: Repair the short to ground in the (V30) S/C Brake Switch Output circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 9
7. (V32) S/C SUPPLY CIRCUIT OPEN
Turn the ignition off.
Disconnect the C3 PCM harness connector.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.
Measure the resistance of the (V32) S/C Supply circuit from the Stop Lamp Switch harness connector to the appropriate terminal of special tool #8815.
Q: Is the resistance above 5.0 ohms?
YES: Repair the open in the (V32) S/C Supply circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 8
8. (V32) S/C SUPPLY CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (V32) S/C Supply circuit in the Stop Lamp Switch harness connector.
Q: Is the resistance below 100 ohms?
YES: Repair the short to ground in the (V32) S/C Supply circuit. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Go To 9
9. PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Q: Were there any problems found?
YES: Repair as necessary. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
NO: Replace and program the Powertrain Control Module. Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test