Massey Ferguson 4354.03 – Engine ECU: DEF Suction Supply Pipe Heater Relay Issue (ECU) / DEF suction line heater relay low side (line relay) open circuit.

The Engine Electronic Management (EEM4) monitoring system has detected an open circuit on the DEF (Diesel Exhaust Fluid) suction line heater relay. This means the circuit responsible for heating the DEF fluid as it is drawn from the tank is broken, which can prevent the DEF from thawing in freezing conditions, leading to emissions derates.

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624
• 4707
• 4708
• 4709
• 4710
• 5710 SL
• 5711 SL
• 5712 SL
• 5713 SL
• 7714
• 7715
• 7715S
• 7716
• 7716S
• 7718
• 7718S
• 7719
• 7720
• 7720S
• 7722
• 7722S
• 7724
• 7724S
• 7726
• 7726S

1. 1

   Check the operation by swapping the DEF suction line heater relay with another known-good relay of the same type in the fuse/relay box to see if the relay itself is defective.

2. 2

   Inspect the wiring harness between the Engine ECU and the DEF suction line heater relay. Look for broken wires, chafing, or disconnected pins that would cause an open circuit.

3. 3

   Test the resistance of the DEF suction line heater element itself (often integrated into the DEF suction tube/head unit) using a multimeter. If the resistance is out of specification (open), the heater is defective.

1. 1

   Power Down

   Turn off the tractor and disconnect the battery isolator switch to ensure no power is running to the ECU.

2. 2

   Locate the Relay

   Access the main fuse/relay box and locate the DEF suction line heater relay (refer to the specific tractor model's fuse diagram).

3. 3

   Replace the Relay

   If the relay was proven faulty during the swap test, install a new OEM relay.

4. 4

   Repair Wiring (If Applicable)

   If the relay is good but the circuit is open, trace the wiring from the ECU to the relay and from the relay to the DEF suction line. Repair any broken wires or replace damaged connector pins.

5. 5

   Replace the DEF Suction Line (If Applicable)

   If the heater element inside the suction line has failed, you must replace the DEF suction line assembly. Disconnect the fluid lines and electrical connector at the DEF tank head unit, remove the assembly, and install the new one.

6. 6

   Clear Codes

   Reconnect the battery, turn the ignition on, and use a diagnostic service tool (like WinEEM4 or AGCO EDT) to clear the stored fault codes and verify the repair.