P0594-SPEED CONTROL SERVO POWER RELAY CIRCUIT

For a complete wiring diagram Refer to Section 8W.

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. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).

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.

Is the DTC Active at this time?

Yes

Go To 2

Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

2.(V32) S/C SUPPLY CIRCUIT

Does the test light illuminate brightly?

Yes

Go To 3

Go To 7

3. STOP LAMP SWITCH

Does the resistance change from below 5.0 ohms to an open circuit?

Yes

Go To 4

Replace the Stop Lamp Switch.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

4.(V30) S/C BRAKE SWITCH OUTPUT

NOTE: It is necessary to PRESS and HOLD the Speed Control Switch in the ON position while checking for voltage.

Does the test light illuminate brightly?

Yes

Replace the S/C Servo.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 5

5.(V30) S/C BRAKE SWITCH OUTPUT CIRCUIT OPEN

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. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 6

6.(V30) S/C BRAKE SWITCH OUTPUT CIRCUIT SHORTED TO GROUND

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. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 9

7.(V32) S/C SUPPLY CIRCUIT OPEN

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.

Is the resistance above 5.0 ohms?

Yes

Repair the open in the (V32) S/C Supply circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 8

8.(V32) S/C SUPPLY CIRCUIT SHORTED TO GROUND

Is the resistance below 100 ohms?

Yes

Repair the short to ground in the (V32) S/C Supply circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Go To 9

9.PCM

NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.

Were there any problems found?

Yes

Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)

Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)