New Holland ENG 3354 – Engine Controller (EDC / Engine ECU): Main Relay 4 (Engine Brake Exhaust Valve) — Short circuit to Ground

The Engine Controller has detected a short to ground on the high side supply #4 circuit, which provides power to the Exhaust Brake flap actuator (controlled via Main Relay 4).

• T7 Series (T7.220, T7.235, T7.250, T7.260, T7.270)
• T8 Series
• CR9090
• CX8080 Elevation
• CX8090 Elevation
• Magnum 235–340 (Series 4)
• Puma series

1. 1

   Visually inspect the wiring harness running from the Engine Controller to Main Relay 4 and the Exhaust Brake flap actuator. Look for chafed insulation, melted wires, or pinch points where the wire might be touching the machine's chassis (ground).

2. 2

   Disconnect the Exhaust Brake flap actuator and Main Relay 4. Use a digital multimeter to check the high side supply #4 circuit for continuity to ground. If continuity to ground is present while disconnected, the wiring harness is shorted.

3. 3

   Test Main Relay 4 and the exhaust brake actuator coil for internal short circuits to ground.

4. 4

   Inspect the connectors at the Engine ECU, relay block, and actuator for water ingress, corrosion, or bent pins that could bridge the power supply to a ground pin.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the negative battery terminal to prevent further electrical damage.

2. 2

   Isolate the Short

   Based on the diagnostic checks, locate the exact point of the short circuit (either in the wiring harness, the relay, or the actuator).

3. 3

   Repair the Wiring

   If the harness is rubbed through and shorting to the chassis, cut out the damaged section of wire, solder in a new section of the correct gauge, and seal it with marine-grade heat shrink. Secure the harness away from sharp edges or hot exhaust components.

4. 4

   Replace Faulty Components

   If Main Relay 4 or the Exhaust Brake flap actuator is internally shorted, remove the defective component and install a new OEM replacement.

5. 5

   Reassemble and Clear Codes

   Reconnect all electrical connectors and the battery. Use a diagnostic scan tool to clear the ENG 3354 fault code from the Engine Controller.

6. 6

   Test Operation

   Start the engine and engage the exhaust brake to verify that the system operates correctly and the fault code does not return.