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
-
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 -
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 -
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). -
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 -
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).
