Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC P0504: Brake Switch Circuit 1-2 CorrelationDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
CHMSL Relay Coil B+ | 1 | 1 | 2 | -- |
Stop Lamp Switch B+ | 1 | 1 | -- | -- |
Stop Lamp Switch Signal | PO504 | PO504 | PO504 | -- |
Stop Lamp Control | 1 | 1 | 2 | -- |
CHMSL Relay Switch Control | 1 | 1 | -- | -- |
CHMSL Relay Ground | -- | 1 | -- | -- |
1. Stop lamps are inoperative 2. Stop lamps are always ON | ||||
Circuit/System Description
The engine control module (ECM) monitors the stop lamp switch signal circuit and the torque converter clutch (TCC) brake switch/cruise control release signal circuit every 100 ms. The ECM monitors the status of the stop lamp switch signal circuit and the TCC brake switch/cruise control signal circuit to see if they match when the brake pedal is pressed or released.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The status of the stop lamp switch input to the ECM, and the TCC brake switch/cruise control input to the ECM do not match for at least 2 seconds continuously, for 10 occurrences. Each time the signals match then do not match a counter increments. When the counter reaches 10 the DTC will set.
Action Taken When the DTC Sets
When DTC P0504 is set the following will occur:
| • | The cruise control is disabled. |
| • | The ECM will function as if the brake pedal is not pressed. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
Conditions for Clearing the DTC
| • | The DTC will clear when the status of the stop lamp switch input to the ECM, and the TCC brake switch/cruise control input to the ECM match for at least 2 seconds continuously for both the pressed position and the released position. |
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
Diagnostic Aids
Aftermarket trailer brake controllers must be disconnected before diagnosing DTC P0504.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- Verify that the scan tool TCC/Cruise Brake Pedal Switch parameter changes between Applied and Released, while pressing and releasing the brake pedal.
- Verify that the scan tool Stoplamp Pedal Switch parameter changes between Applied and Released, while pressing and releasing the brake pedal.
| ⇒ | If the parameter does not change as the brake pedal is applied and released, refer to TCC/Cruise Brake Switch Malfunction. |
| ⇒ | If the parameter does not change as the brake pedal is applied and released, refer to Stop Lamp Switch Malfunction. |
Circuit/System Testing
TCC/Cruise Brake Switch Malfunction
- Ignition OFF, disconnect the harness connector at the stop lamp switch.
- Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal C and ground.
- Verify the scan tool TCC/Cruise Brake Pedal Switch parameter is Released.
- Install a 10A fused jumper wire between the control circuit terminal D and the B+ circuit terminal C. Verify the scan tool TCC/Cruise Brake Pedal Switch parameter is Applied.
- If all circuits test normal, test or replace the stop lamp switch.
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. |
| ⇒ | If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM. |
| ⇒ | If not the specified value, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM. |
Stop Lamp Switch Malfunction
- Ignition OFF, disconnect the harness connector at the stop lamp switch.
- Ignition ON, verify that a test lamp illuminates between the appropriate B+ circuit terminal listed below and ground.
- Verify the scan tool Stoplamp Pedal Switch parameter is Released.
- Install a 10A fused jumper wire between B+ and the appropriate signal circuit terminal listed below Verify the scan tool Stoplamp Pedal Switch parameter is Applied.
- If all circuits test normal, test or replace the stop lamp switch.
| • | B+ terminal E - with C4 and JE3 |
| • | B+ terminal E - with C7/C8 and JE4 |
| • | B+ terminal B - with C5/C6/C7 and JE3 |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the stop lamp switch. |
| ⇒ | If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM. |
| • | Stop lamp switch signal terminal F- with C4 and JE3 |
| • | Stop lamp switch signal terminal F - with C7/C8 and JE4 |
| • | Stop lamp switch signal terminal A - with C5/C6/C7 and JE4 |
| ⇒ | If not the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for ECM replacement, setup, and programming
