P0478

P0478-HIGH VOLTAGE ON THE ENGINE BRAKE DRIVER


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

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test

1. RELAY
Ignition on, engine not running.
With the scan tool, actuate the Engine Brake Driver Relay.

Q: Can you hear the Relay clicking?

YES: Go To 2
NO: Go To 3

2. RELAY LOOSE
While the relay is clicking, wiggle the wiring harness and connectors.

Q: Does this interrupt the clicking?

YES: Repair the loose connection. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
NO: Go To 3

3. Engine Brake Driver Control Circuit
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.

Q: Is the voltage less than 1 volt?

YES: Go To 4
NO: Repair Engine Brake Driver Control Circuit shorted to voltage. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1

4. Engine brake relay
Measure the resistance between terminals 85 and 86 of the engine brake relay.

Q: Is the resistance less than 10 ohms?

YES: Replace the engine brake relay. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
NO: Go To 5

5. ECM
Reconnect the ECM harness connectors.
Reinstall the Engine Brake relay.
Ignition on, engine not running.
While monitoring with the scan tool, remove the Engine Brake Driver Relay.

Q: Did P0477 set?

YES: Refer to the INTERMITTENT CONDITION Symptom (Diagnostic Procedure).
NO: Replace the ECM. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1