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  • P0478 High Voltage On The Engine Brake Driver

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    P0478 HIGH VOLTAGE ON THE ENGINE BRAKE DRIVER

    When Monitored and Set Condition:

    When Monitored: When the ignition is on.
    Set Condition: When the signal from the engine brake driver output does not match the signal from the engine
    brake driver feedback.

    POSSIBLE CAUSES

    • RELAY LOOSE
    • ENGINE BRAKE DRIVER CONTROL CIRCUIT SHORTED TO VOLTAGE
    • ENGINE BRAKE RELAY
    • INTERMITTENT CONDITION
    • ECM

    DIAGNOSTIC PROCEDURE

    1. Ignition on, engine not running. With the DRBIII®, actuate the Engine Brake Driver Relay. Can you hear the Relay clicking?
      Yes --> Go To 2
      No --> Go To 3
    2. While the relay is clicking, wiggle the wiring harness and connectors. Does this interrupt the clicking?
      Yes --> Repair the loose connection. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
      No --> Go To 3
    3. Turn the ignition off. Remove the Engine Brake Driver Relay. Disconnect the ECM harness connectors. Check connectors - Clean/repair as necessary. Measure the voltage of the Engine Brake Driver Control Circuit between the relay terminal and battery negative. Is the voltage less than 1 volt?
      Yes --> Go To 4
      No --> Repair Engine Brake Driver Control Circuit shorted to voltage. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
    4. Measure the resistance between terminals 85 and 86 of the engine brake relay. Is the resistance less than 10 ohms?
      Yes --> Replace the engine brake relay. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
      No --> Go To 5
    5. Reconnect the ECM harness connectors. Reinstall the Engine Brake relay. Ignition on, engine not running. While monitoring with the DRBIII®, remove the Engine Brake Driver Relay. Did P0477 set?
      Yes --> Refer to the SYMPTOM: INTERMITTENT CONDITION Symptom (Diagnostic Procedure). Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
      No --> Replace the ECM. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).

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