P0477

P0477-LOW 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
- 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

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test

1. RELAY CLICKING
Turn the engine off (ignition on).
With the scan tool, actuate the exhaust brake relay.

Q: Can you hear the Relay clicking?

YES: Go To 2
NO: Go To 3

2. WIRING HARNESS
With the scan tool, actuate the exhaust brake relay.
While the relay is clicking, wiggle the wiring harness and connectors throughout the circuit.

Q: Does this interrupt the clicking?

YES: Repair or replace the wiring harness. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1
NO: Go To 3

3. Engine Brake Driver Relay
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.

Q: Is the resistance less than 100 Ohms?

YES: Go To 4
NO: Replace the Engine Brake Driver Relay. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1

4. FUSED B+ OPEN
Ignition on, engine not running.
Measure the voltage of the Fused B+ Supply circuit at the Engine Brake Relay.

Q: Is the voltage within 10% of battery voltage?

YES: Go To 5
NO: Repair the open B+ circuit. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1

5. ENGINE BRAKE DRIVER SIGNAL CIRCUIT OPEN
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.

Q: 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 the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1

6. ENGINE BRAKE DRIVER SIGNAL CIRCUIT SHORTED TO BATTERY NEGATIVE
Measure the resistance of the Engine Brake Driver signal circuit between the Relay connector and battery negative.

Q: Is the resistance greater than 100k Ohms?

YES: Go To 7
NO: Repair Engine brake driver shorted to Battery negative. Perform the POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). Powertrain Verification Test - Ver 1

7. ECM
Reconnect the ECM harness connectors.
Using the scan tool, actuate the Engine Brake Driver Relay.
While monitoring with the scan tool, use a jumper wire to connect 12 volts to the relay signal circuit with the relay disconnected.

Q: Did the DTC P0478?

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