Circuit Description
The signal of the stop lamp switch is used to determine whether the brake system is abnormal or not. The stop lamp switch has a duplex system (signals STP and ST1) to detect an abnormality. When the signals of depressing and releasing the brake pedal are detected simultaneously, the engine control module (ECM) interprets this as a malfunction of the stop lamp switch.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
The brake pedal is released, if the status of the stop lamp switch input signal to the ECM does not match for at least 0.5 seconds or more 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 control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
Conditions for Clearing the DTC
| • | The DTC will clear when the status of the stop lamp switch input signals to the ECM match for at least 0.5 seconds continuously for both the pressed position and the released position. |
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
| • | Inspect for proper adjustment of the stop lamp switch. Refer to Stop Lamp Switch Adjustment . |
| • | Check for intermittents and poor connections. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Exterior Lights Schematics and Cruise Control Schematics Connector End View Reference: Lighting Systems Connector End Views | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic Starting Point - Lighting Systems in Vehicle DTC Information |
2 |
Important: The stop lamp switch must be adjusted correctly for proper operation. Refer to Stop Lamp Switch Adjustment . Check to see if the stop lamps operate correctly. Do the stop lamps operate correctly? | Go to Step 3 | Go to Stop Lamps Inoperative |
3 |
Does the Brake Pedal Switch parameter display change with the brake pedal position? | Go to Step 6 | Go to Step 4 |
4 |
Is the voltage below 1.5 volts? | Go to Step 5 | Go to Step 6 |
5 | With the brake pedal released, use a digital multimeter, test for voltage between PCM connector C1 terminal 3 and the PCM connector C3 terminal 11. Refer to Circuit Testing in Wiring Systems. Is the voltage between 7.5 volts and 14 volts? | Go to Step 6 | Go to Step 7 |
6 | Test for intermittent circuit problems between the brake switch and the PCM. Refer to Testing for Electrical Intermittents and Wiring Repairs in Wiring Systems Did you find and complete the repair? | Go to Step 9 | Go to Step 8 |
7 | Repair the short or high resistance in the stop lamp signal circuit between the PCM connector C1 terminal 3 and the PCM connector C3 terminal 11. Refer to Wiring Repairs in Wiring Systems Did you find and complete the repair? | Go to Step 9 | Go to Step 2 |
8 | Replace the PCM. Refer to Powertrain Control Module Replacement --LV6 or Powertrain Control Module Replacement -- LNK in Engine Controls Did you complete the replacement? | Go to Step 9 | Go to Step 2 |
9 |
Does the DTC reset? | Go to Step 2 | System OK |
