Massey Ferguson E4355.04 – Engine Control Unit (ECU) / AGCO SISU POWER EEM4: DEF Return Pipe Heater Relay Issue (ECU)

The controller has detected an open circuit, a broken connection, or a short to ground on the high side of the relay that controls the heating element for the Diesel Exhaust Fluid (DEF) return/backflow pipe.

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624
• MF 5608
• MF 5609
• MF 5610
• MF 5611
• MF 5612
• MF 5613
• MF 7614
• MF 7615
• MF 7616
• MF 7618
• MF 7619
• MF 7620
• MF 7622
• MF 7624
• MF 7626

1. 1

   Inspect the fuse block for any blown fuses related to the DEF heating system or emissions relays.

2. 2

   Locate the DEF return pipe heater relay. Pull the relay and inspect the socket pins for corrosion, pushed-out pins, or signs of overheating/melting.

3. 3

   Bench-test the DEF return pipe heater relay to see if the internal coil is open (infinite resistance) or if the contacts are failing to close when voltage is applied.

4. 4

   Check the wiring harness continuity between the EEM4 ECU and the relay socket, as well as from the relay to the DEF return pipe heater. Look for chafed wires, broken lines, or loose machine grounds.

1. 1

   Power Down

   Turn off the ignition, remove the key, and disconnect the battery to prevent electrical shorts during repair.

2. 2

   Access the Relay Panel

   Locate the emissions/DEF relay block (refer to the specific tractor model's fuse/relay diagram).

3. 3

   Replace or Repair

   If the diagnostic checks revealed a faulty relay (open coil), replace the DEF return pipe heater relay with a new OEM relay. If the relay is functional but the wiring is damaged, repair the broken wire in the harness using proper weather-sealed connectors.

4. 4

   Reassemble and Reconnect

   Seat the relay firmly into the socket and reconnect the battery.

5. 5

   Clear Codes and Test

   Turn the ignition on. Use a diagnostic service tool (such as the AGCO WinEEM3s/EEM4 Service Tool) to clear the E4355.04 / SPN 4355 FMI 4 fault code. Run the engine and monitor the DEF heater system to ensure the fault does not return.