P0478

P0478-HIGH VOLTAGE ON THE ENGINE BRAKE DRIVER

For complete wiring diagrams refer to Diagrams/Electrical.


- 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.







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.

Can you hear the Relay clicking?

Yes

- Go To2

No

- Go To3

2. RELAY LOOSE

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. Powertrain Verification Test

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.

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. Powertrain Verification Test

4. ENGINE BRAKE RELAY

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. Powertrain Verification Test

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.

Did P0477 set?

Yes

- Refer to the INTERMITTENT CONDITION Diagnostic Procedure. Intermittent Condition

No

- Replace the ECM.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test