P0504-BRAKE SWITCH SIGNAL CIRCUITS PLAUSIBILITY WITH REDUNDANT CONTACT
For a complete wiring diagram Refer to Section 8W
- 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.
| Possible Causes |
| INTERMITTENT CONDITION |
| BRAKE LAMP SWITCH - SENSE CKT OPEN |
| BRAKE LAMP SWITCH FUSED B+ CIRCUIT OPEN |
| BRAKE SWITCH SENSE CIRCUIT SHORTED TO GROUND |
| BRAKE LAMP SWITCH - OUTPUT OPEN |
| BRAKE SWITCH SENSE CIRCUIT OPEN |
| BRAKE SWITCH SENSE GROUND CIRCUIT OPEN |
| BRAKE LAMP SWITCH OUTPUT CIRCUIT SHORTED TO VOLTAGE |
| BRAKE LAMP SWITCH OUTPUT CIRCUIT OPEN |
| ENGINE CONTROL MODULE - BRAKE SWITCH SENSE |
| ENGINE CONTROL MODULE - INTERNAL |
| ENGINE CONTROL MODULE - PRIMARY BRAKE SIGNAL |
Diagnostic Test
1. CHECK THE PRIMARY BRAKE SWITCH STATUS WITH THE SCAN TOOLNOTE: If the ECM detects and stores a DTC, the ECM also stores the engine/vehicle operating conditions under which the DTC was set. Some of these conditions are displayed on the scan tool at the same time the DTC is displayed.
NOTE: Before erasing stored DTCs, record these conditions. Attempting to duplicate these conditions may assist when checking for an active DTC.
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 To10
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
- Refer to the *CHECKING FOR AN INTERMITTENT DTC Diagnostic Procedure. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)
No
- Go To3
3. BRAKE SWITCH SENSE CIRCUIT VOLTAGE
Turn the ignition off.
Disconnect the Brake Lamp Switch harness connector.
Turn the ignition on.
Measure the voltage between the Brake Switch Sense circuit and ground.
Is the voltage above 9.0 volts?
Yes
- Go To4
No
- Go To7
4. BRAKE LAMP SWITCH - SENSE CKT OPEN
While monitoring the SECONDARY BRAKE SWITCH status with the scan tool, connect a jumper wire between ground and the Secondary Brake Switch Sense circuit.
Does the scan tool display change from PRESSED to RELEASED?
Yes
- Adjust or replace the Brake Lamp Switch in accordance with the Service Information.
- Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
No
- Go To5
5. BRAKE SWITCH SENSE GROUND CIRCUIT OPEN
Turn the ignition off.
Measure the resistance between ground and the Secondary Brake Switch Ground circuit.
Is the resistance below 10.0 ohms?
Yes
- Go To6
No
- Repair the Brake Switch Sense Ground circuit for an open.
- Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
6. ENGINE CONTROL MODULE - INTERNAL
If there are no possible causes remaining, view repair.
Repair
- Replace and program the Engine Control Module in accordance with the Service Information.
- Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
7. BRAKE SWITCH SENSE CIRCUIT SHORTED TO GROUND
Turn the ignition off.
Disconnect the ECM harness connectors.
Measure the resistance between ground and the Brake Switch Sense circuit.
Is the resistance above 1000 ohms?
Yes
- Go To8
No
- Repair the Brake Switch Sense circuit for a short to ground.
- Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
8. BRAKE SWITCH SENSE CIRCUIT OPEN
Measure the resistance of the Brake Switch Sense circuit.
Is the resistance below 10.0 ohms?
Yes
- Go To9
No
- Repair the Brake Switch Sense circuit for an open.
- Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
9. ENGINE CONTROL MODULE - SECONDARY BRAKE SIGNAL
If there are no possible causes remaining, view repair.
Repair
- Replace and program the Engine Control Module in accordance with the Service Information.
- Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
10. BRAKE LAMP SWITCH 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 Fused B+ circuit.
Does the test light illuminate brightly?
Yes
- Go To11
No
- Repair the Brake Lamp Switch Fused B+ circuit for an open.
- Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
11. BRAKE LAMP SWITCH - PRIMARY OPEN
Disconnect the Brake Lamp Switch harness connector.
Turn the ignition on.
While monitoring the PRIM BRAKE SWITCH status with the Scan Tool, connect a jumper wire between the Brake Lamp Switch Output circuit and the Fused B(+) circuit.
Does the scan tool display change from RELEASED to PRESSED?
Yes
- Adjust or replace the Brake Lamp Switch in accordance with the Service Information.
- Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
No
- Go To12
12. BRAKE LAMP SWITCH OUTPUT CIRCUIT SHORTED TO VOLTAGE
Turn the ignition off.
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 Brake Lamp Switch Output circuit and ground.
Is the voltage above 1.0 volt?
Yes
- Repair the Brake Lamp Switch Output circuit for a short to voltage.
- Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
No
- Go To13
13. BRAKE LAMP SWITCH OUTPUT CIRCUIT OPEN
Turn the ignition off.
Measure the resistance of the Brake Lamp Switch Output circuit.
Is the resistance below 10.0 ohms?
Yes
- Replace and program the Engine Control Module in accordance with the Service Information.
- Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
No
- Repair the Brake Lamp Switch Output circuit for an open.
- Perform the ECM Verification Test Ver. 1 (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).