Massey Ferguson 4340.03 – ECU: DEF Suction Supply Pipe Heater Resistance Is High (ECU)

The system has detected that the electrical resistance in the DEF (Diesel Exhaust Fluid) suction line heater circuit is higher than the specified threshold. This typically indicates an open circuit, a broken wire, a faulty relay, or a burned-out heating element inside the DEF suction pipe. The heater is necessary to thaw frozen DEF in cold climates so it can be pumped to the injector.

• 4710
• 7724S
• 5712SL
• Interim Tier 4 (2012-2015)
• 7722
• 7722S
• 7615
• 5613
• 5713SL
• 7720S
• 7716
• 7718
• T4
• 7715
• 5710SL
• 7726
• 7616
• 7618
• 5608
• 4708
• 7619
• 7626
• 7726S
• 7624
• 4707
• 4709
• 5711SL
• 7614
• 7718S
• 5610
• 7620
• 7719
• 7714
• 7716S
• T4 (2015-2021)
• 5612
• 7622
• 7720
• Tier 4 (2015-2021)
• 5611
• 7715S
• 5609
• 7724

1. 1

   Swap the DEF suction line heater relay (main relay) in the fuse/relay box with a known good relay of the same type to see if the fault code changes or clears.

2. 2

   Visually inspect the wiring harness running from the ECU to the DEF suction line heater. Look for chafed wires, corrosion at the connectors, or loose pins.

3. 3

   Disconnect the electrical connector at the DEF suction line. Using a multimeter, measure the resistance across the heater pins. If the multimeter reads OL (open loop) or an extremely high resistance, the heating element inside the pipe has failed.

4. 4

   With the ignition on (and conditions met for heater activation), check for voltage at the harness side of the connector to ensure the ECU is sending power to the line.

1. 1

   Preparation

   Turn off the tractor, remove the key, and disconnect the negative battery cable to prevent electrical shorts.

2. 2

   Access the DEF Tank

   Locate the DEF tank and the suction line assembly (the line running from the DEF tank header to the DEF pump).

3. 3

   Disconnect Lines

   Carefully disconnect the electrical connector for the suction line heater. Depress the quick-release tabs on the DEF fluid fittings to disconnect the suction pipe from both the tank header and the pump. Note: Have a catch pan ready, as residual DEF will spill.

4. 4

   Remove the Pipe

   Unclip the suction pipe from any retaining brackets along the chassis.

5. 5

   Install the New Pipe

   Route the new DEF suction line (which contains the integrated heater) along the same path. Secure it into the retaining clips.

6. 6

   Reconnect

   Snap the fluid fittings onto the DEF tank and pump until they click securely. Reconnect the electrical connector.

7. 7

   Finalize

   Reconnect the battery. Turn the ignition on and use a diagnostic service tool to clear the 004340.03 fault code. Run the tractor to ensure no leaks are present and the code does not return.