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).