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P0504







P0504-BRAKE SWITCH SIGNAL CIRCUITS PLAUSIBILITY WITH REDUNDANT CONTACT





For a complete wiring diagram Consult 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.Initial Inspection and Diagnostic Overview

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 To2

No

- Go To11

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 To3

No

- Go To4

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.
Search for 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. Verification Tests

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 To5

No

- Go To8

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. Verification Tests

No

- Go To6

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 To7

No

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

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.Verification Tests

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 To9

No

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

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 To10

No

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

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. Verification Tests

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 To12

No

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

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. Verification Tests

No

- Go To13

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. Verification Tests

No

- Go To14

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. Verification Tests

No

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