Massey Ferguson E4355.03 – Engine Control Unit (ECU): DEF Return Pipe Heater Relay Issue (ECU)

Low side, open circuit relay AdBlue™ or DEF preheater return line. The ECU has detected an open circuit on the low side of the DEF return line heater relay's circuit.

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

1. 1

   Locate the DEF return pipe heater relay in the fuse/relay panel and swap it with a known good relay or test it with a multimeter for an open internal coil.

2. 2

   Inspect the wiring harness between the ECU, the relay box, and the DEF return line for chafed wires, broken lines, or disconnected plugs on the low-side circuit.

3. 3

   Check the quick connectors and electrical plugs at the DEF pump module and along the heated return line for corrosion, moisture, or backed-out pins.

4. 4

   Unplug the DEF return line heater and measure its resistance with a multimeter to ensure the heating element itself has not failed open.

1. 1

   Power Down

   Turn off the tractor and disconnect the negative battery terminal to prevent electrical shorts during repair.

2. 2

   Access the Relay

   Open the fuse/relay box and locate the DEF return pipe heater relay (refer to the fuse box diagram on the panel lid or operator's manual).

3. 3

   Replace or Repair

   If the relay tested faulty (open coil), replace it with a new OEM 12V relay. If the relay is good, trace the low-side wire from the relay socket back to the ECU. Repair any broken wires or replace damaged connector pins using standard wiring repair procedures.

4. 4

   Inspect the Line

   If the wiring to the relay is intact, verify the connection at the DEF return line itself. If the heating element inside the line is broken (open circuit), the entire DEF heated return line must be replaced.

5. 5

   Reassemble and Clear Codes

   Reconnect the battery, turn the key to the ON position, and use an AGCO diagnostic tool (EDT) to clear the E4355.03 fault code. Run the tractor to verify the code does not return.