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For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2007 🢒 Isuzu H-Series 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0504

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 Correlation

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 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 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

    •  Engine Controls Schematics
    •  Cruise Control Schematics
    •  Power Distribution Schematics

Connector End View Reference

Lighting Systems Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for Scan Tool Information

Circuit/System Verification
  1. Verify that the scan tool TCC/Cruise Brake Pedal Switch parameter changes between Applied and Released, while pressing and releasing the brake pedal.
    2. ⇒If the system does not perform as specified, refer to TCC/Cruise Brake Pedal Switch Malfunction.
  2. Verify that the scan tool Stoplamp Pedal Switch parameter changes between Applied and Released, while pressing and releasing the brake pedal.
    3. ⇒If the system does not perform as specified, refer to Stop Lamp Pedal Switch Malfunction.

Circuit/System Testing

TCC/Cruise Brake Pedal Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
  2. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal C and ground.
    3. ⇒If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  3. Verify the scan tool TCC/Cruise Brake Pedal Switch parameter is Released.
    4. ⇒If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Install a 10A fused jumper wire between the control circuit terminal D and the ignition circuit terminal C. Verify the scan tool TCC/Cruise Brake Pedal Switch parameter is Applied.
    5. ⇒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.
  5. If all circuits test normal, test or replace the stop lamp switch.

Stop Lamp Pedal Switch Malfunction

  1. Ignition OFF, disconnect the harness connector at the stop lamp switch.
  2. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal E (C4 w/JE3 or C7/C8 w/JE4) or B (C5/C6/C7 w/JE3) and ground.
    3. ⇒If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test or replace the stop lamp switch.
  3. Verify the scan tool Stoplamp Pedal Switch parameter is Released.
    4. ⇒If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  4. Install a 10A fused jumper wire between the control circuit terminal A (C5/C6/C7 w/JE4) or F (C4 w/JE3 or C7/C8 w/JE4) and the ignition circuit terminal E (C4 w/JE3 or C7/C8 w/JE4) or B (C5/C6/C7 w/JE3). Verify the scan tool Stoplamp Pedal Switch parameter is Applied.
    5. ⇒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.
  5. If all circuits test normal, test or replace the stop lamp switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Stop Lamp Switch Replacement