Massey Ferguson 4342.04 – Engine Control Unit (ECU): DEF Return Pipe Heater Resistance Is Low (ECU)

The system has detected that the electrical resistance in the DEF (Diesel Exhaust Fluid) return pipe heater circuit is below the normal operating threshold. A "low resistance" reading typically indicates a short circuit within the heating element itself, or a short-to-ground/short-between-wires in the wiring harness supplying power to the heater.

• 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

   Inspect the wiring harness and connectors leading to the DEF return line heater for chafed wires, melted insulation, or corrosion.

2. 2

   Perform a resistance test on the DEF return pipe heater element (should read between 3 to 15 ohms; near 0 ohms indicates an internal short).

3. 3

   Test the harness side for continuity to ground to ensure the short isn't in the tractor's main wiring harness.

4. 4

   Check the cab electric center/fuse box for blown DEF system heating fuses or a damaged DEF line heater relay.

1. 1

   Power Down

   Turn off the tractor, remove the key, and disconnect the battery to prevent electrical spikes.

2. 2

   Clean the Area

   Thoroughly clean the area around the DEF supply module (pump) and the DEF tank to prevent dirt from entering the SCR system.

3. 3

   Disconnect Electricals

   Unplug the electrical connector for the DEF return line heater.

4. 4

   Disconnect Fluid Lines

   Depress the quick-release tabs and disconnect the DEF return line from the DEF metering/supply module and the DEF tank. Note: Immediately cap or block the open ports on the pump and tank to prevent debris contamination.

5. 5

   Remove the Old Line

   Unclip the return line from its routing brackets along the chassis and remove it.

6. 6

   Install the New Line

   Route the new DEF return line assembly in the exact same path, ensuring it is not pinched or rubbing against sharp edges.

7. 7

   Reconnect

   Snap the quick-connect fluid fittings into place and plug in the heater's electrical connector.

8. 8

   Replace Fuses

   Replace any fuses that were blown by the short circuit.

9. 9

   Clear Codes and Test

   Reconnect the battery, turn on the ignition, and use a diagnostic tool to clear the 004342.04 fault code. Run an SCR system test or allow the tractor to warm up to verify the code does not return.