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  • P0477 Low Voltage on The Engine Brake Driver

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    P0477 LOW 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

    • WIRING HARNESS
    • ENGINE BRAKE DRIVER RELAY
    • FUSED B+ OPEN
    • ENGINE BRAKE DRIVER SIGNAL CIRCUIT OPEN
    • INTERMITTENT CONDITION
    • ENGINE BRAKE DRIVER SIGNAL CIRCUIT SHORTED TO BATTERY NEGATIVE
    • ECM

    DIAGNOSTIC PROCEDURE

    1. Turn the engine off (ignition on). With the DRBIII®, actuate the exhaust brake relay. Can you hear the Relay clicking?
      Yes --> Go To 2
      No --> Go To 3
    2. With the DRBIII®, actuate the exhaust brake relay. While the relay is clicking, wiggle the wiring harness and connectors throughout the circuit. Does this interrupt the clicking?
      Yes --> Repair or replace the wiring harness. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
      No --> Go To 3
    3. Remove the Engine Brake Driver Relay. Check connectors - Clean/repair as necessary. Measure the resistance between terminals 86 and 85 of the engine brake relay. Is the resistance less than 100 Ohms?
      Yes --> Go To 4
      No --> Replace the Engine Brake Driver Relay. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
    4. Ignition on, engine not running. Measure the voltage of the Fused B+ Supply circuit at the Engine Brake Relay. Is the voltage within 10% of battery voltage?
      Yes --> Go To 5
      No --> Repair the open B+ circuit. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
    5. Turn the ignition off. Disconnect the ECM harness connectors. Check connectors - Clean/repair as necessary. Measure the resistance of the Engine Brake Driver signal circuit between the Relay harness connector and the ECM harness connector. Is the resistance less than 10 Ohms?
      Yes --> Go To 6
      No --> Repair the open Engine Brake driver circuit open from relay to ECM. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
    6. Measure the resistance of the Engine Brake Driver signal circuit between the Relay connector and battery negative. Is the resistance greater than 100k Ohms?
      Yes --> Go To 7
      No --> Repair Engine brake driver shorted to Battery negative. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
    7. Reconnect the ECM harness connectors. Using the DRBIII®, actuate the Engine Brake Driver Relay. While monitoring with the DRBIII®, use a jumper wire to connect 12 volts to the relay signal circuit with the relay disconnected. Did the DTC P0478?
      Yes --> Refer to the SYMPTOM: INTERMITTENT CONDITION Symptom (Diagnostic Procedure). Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).
      No --> Replace ECM. Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL).

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