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P0504






P0504-BRAKE SWITCH SIGNAL CIRCUITS PLAUSIBILITY WITH REDUNDANT CONTACT





For a complete wiring diagram refer to Diagrams/Electrical

- When Monitored:

With the ignition on.

- Set Condition:

The Primary Brake Switch Signal and Secondary Brake Switch Signal inputs to the ECM do not agree for 2 minutes.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.


Diagnostic Test

1. CHECK THE PRIMARY BRAKE SWITCH STATUS

Turn the ignition on.

While observing the PRIMARY BRAKE SWITCH status on the scan tool display, press and release the brake pedal several times.

Does the scan tool display PRIMARY BRAKE SWITCH: PRESSED and RELEASED for the appropriate pedal position?

Yes

- Go To 2

No

- Go To 11


2. CHECK THE SECONDARY BRAKE SWITCH STATUS WITH THE SCAN TOOL

While observing the SECONDARY BRAKE SWITCH status on the scan tool display, press and release the brake pedal several times.

Does the scan tool display SECONDARY BRAKE SWITCH: PRESSED and RELEASED for the appropriate pedal position

Yes

- Go To 3

No

- Go To 4


3. INTERMITTENT CONDITION

WARNING: WHEN THE ENGINE IS OPERATING, DO NOT STAND IN A DIRECT LINE WITH THE FAN. DO NOT PUT YOUR HANDS NEAR THE PULLEYS, BELTS OR FAN. DO NOT WEAR LOOSE CLOTHING.

NOTE: The conditions that set the DTC are not present at this time. The following list may help in identifying the intermittent condition.

With the engine running at normal operating temperature, monitor the scan tool parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set.

Review the DTC When Monitored and Set Conditions. If possible, try to duplicate the conditions under which the DTC was set.

Refer to any Technical Service Bulletins (TSB) that may apply.

Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires.

Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.

Were any of the above conditions present?

Yes

- Repair as necessary.
- Perform the ECM Verification Test Ver. 1. ECM Verification Test

No

- Test Complete.


4. (B16) SECONDARY BRAKE SWITCH SIGNAL CIRCUIT VOLTAGE





Turn the ignition off.

Disconnect the Brake Lamp Switch harness connector.

Turn the ignition on.

Measure the voltage between ground and the (B16) Secondary Brake Switch Signal circuit in the Brake Lamp Switch harness connector.

Is the voltage above 9.0 volts?

Yes

- Go To 5

No

- Go To 8


5. BRAKE SWITCH - SECONDARY SIGNAL CKT OPEN





While monitoring the SECONDARY BRAKE SWITCH status with the scan tool, connect a jumper wire between ground and the Secondary Brake Switch Signal circuit.

Does the scan tool display change from PRESSED to RELEASED?

Yes

- Adjust or replace the Brake Lamp Switch.
- Perform the ECM Verification Test Ver. 1. ECM Verification Test

No

- Go To 6


6. (Z904) GROUND CIRCUIT OPEN





Turn the ignition off.

Remove the jumper wire.

Disconnect the Brake Lamp Switch harness connector.

Measure the resistance between ground and the (Z904) Ground circuit in the Brake Lamp Switch harness connector.

Is the resistance below 10.0 ohms?

Yes

- Go To 7

No

- Repair the (Z904) Ground circuit for an open.
- Perform the ECM Verification Test Ver. 1. ECM Verification Test


7. ENGINE CONTROL MODULE - INTERNAL

If there are no possible causes remaining, view repair.

Repair

- Replace and program the Engine Control Module.
- Perform the ECM VERIFICATION TEST. ECM Verification Test


8. (B16) SECONDARY BRAKE SWITCH SIGNAL CIRCUIT SHORTED TO GROUND





Turn the ignition off.

Disconnect the ECM harness connectors.

Measure the resistance between ground and the (B16) Secondary Brake Switch Signal circuit in the Brake Lamp Switch harness connector.

Is the resistance above 1000 ohms?

Yes

- Go To 9

No

- Repair the (B16) Secondary Brake Switch Signal circuit for a short to ground.
- Perform the ECM Verification Test Ver. 1. ECM Verification Test


9. (B16) SECONDARY BRAKE SWITCH SIGNAL CIRCUIT OPEN





Measure the resistance of the (B16) Secondary Brake Switch Signal circuit between the Brake Lamp Switch harness connector and the Engine Control Module harness connector.

Is the resistance below 10.0 ohms?

Yes

- Go To 10

No

- Repair the (B16) Secondary Brake Switch Signal circuit for an open.
- Perform the ECM Verification Test Ver. 1. ECM Verification Test


10. ENGINE CONTROL MODULE - SECONDARY BRAKE SIGNAL

If there are no possible causes remaining, view repair.

Repair

- Replace and program the Engine Control Module.
- Perform the ECM Verification Test Ver. 1. ECM Verification Test


11. (A103) FUSED B+ CIRCUIT OPEN





Turn the ignition off.

Disconnect the Brake Lamp Switch harness connector.

Using a 12-volt test light connected to ground, check the (A103) Fused B+ circuit in the Brake Lamp Switch harness connector.

Does the test light illuminate brightly?

Yes

- Go To 12

No

- Repair the (A103) Fused B+ circuit for an open.
- Perform the ECM Verification Test Ver. 1. ECM Verification Test


12. BRAKE LAMP SWITCH - PRIMARY SIGNAL OPEN





Turn the ignition on.

While monitoring the PRIM BRAKE SWITCH status with the scan tool, connect a jumper wire between the Primary Brake Switch Signal circuit and the Fused B(+) circuit.

Does the scan tool display change from RELEASED to PRESSED?

Yes

- Adjust or replace the Brake Lamp Switch.
- Perform the ECM Verification Test Ver. 1. ECM Verification Test

No

- Go To 13


13. (L950) PRIMARY BRAKE SWITCH SIGNAL CIRCUIT SHORTED TO VOLTAGE





Turn the ignition off.

Remove the jumper wire.

Disconnect the ECM harness connectors.

Remove the ASD Relay from the PDC.

Connect a jumper wire between cavity 30 and cavity 87 of the ASD Relay connector.

Turn the ignition on.

Measure the voltage between the (L950) Primary Brake Switch Signal circuit and ground in the Brake Switch harness connector.

Is the voltage above 1.0 volt?

Yes

- Repair the (L950) Primary Brake Switch Signal circuit for a short to voltage.
- Perform the ECM Verification Test Ver. 1. ECM Verification Test

No

- Go To 14


14. (L950) PRIMARY BRAKE SWITCH SIGNAL CIRCUIT OPEN





Turn the ignition off.

Remove the jumper wire and install the ASD relay.

Measure the resistance of the (L950) Primary Brake Switch Signal circuit in the Brake Switch harness connector.

Is the resistance below 10.0 ohms?

Yes

- Replace and program the Engine Control Module.
- Perform the ECM Verification Test Ver. 1. ECM Verification Test

No

- Repair the (L950) Primary Brake Switch Signal circuit for an open.
- Perform the ECM Verification Test Ver. 1. ECM Verification Test
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