Dodge Ram Truck 1500-2500-3500. Manual — part 939

P0594-SPEED CONTROL SERVO POWER RELAY CIRCUIT (CONTINUED)

For the Engine circuit diagram (Refer to 9 - ENGINE - SCHEMATICS AND DIAGRAMS).

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.
Ignition on, engine not running.

With a scan tool, read DTCs.

Is the DTC active at this time?

Yes

>> Go To 2

No

>> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.

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

2.

(V32) S/C SUPPLY CIRCUIT

Turn the ignition off.

Disconnect the Stop Lamp Switch harness connector.

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.

Does the test light illuminate brightly?

Yes

>> Go To 3

No

>> Go To 7

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ENGINE - ELECTRICAL DIAGNOSTICS - 3.7L/4.7L/5.7L

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P0594-SPEED CONTROL SERVO POWER RELAY CIRCUIT (CONTINUED)

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.

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. (Refer
to 9 - ENGINE - STANDARD PROCEDURE)

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.

Does the test light illuminate brightly?

Yes

>> Replace the S/C Servo.

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

No

>> Go To 5

DR/DH

ENGINE - ELECTRICAL DIAGNOSTICS - 3.7L/4.7L/5.7L

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P0594-SPEED CONTROL SERVO POWER RELAY CIRCUIT (CONTINUED)

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 har-
ness connector.

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)

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.

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)

No

>> Go To 9

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ENGINE - ELECTRICAL DIAGNOSTICS - 3.7L/4.7L/5.7L

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P0594-SPEED CONTROL SERVO POWER RELAY CIRCUIT (CONTINUED)

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.

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)

No

>> Go To 8

8.

(V32) S/C SUPPLY CIRCUIT SHORTED TO GROUND

Measure the resistance between ground and the (V32) S/C Supply cir-
cuit in the Stop Lamp Switch harness connector.

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)

No

>> Go To 9

DR/DH

ENGINE - ELECTRICAL DIAGNOSTICS - 3.7L/4.7L/5.7L

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