Massey Ferguson 4340.05 – Engine ECU: DEF Suction Supply Pipe Heater Open Circuit

The Engine Control Unit (ECU) has detected an "open circuit" in the control circuit for the Diesel Exhaust Fluid (DEF) suction line heater. This means there is a physical break in the electrical path—most commonly a broken wire, a disconnected or corroded plug, or a burned-out heating element inside the DEF suction hose itself.

• 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
• 5710 SL
• 5711 SL
• 5712 SL
• 5713 SL

1. 1

   Visually inspect the DEF suction line (from the DEF tank to the supply pump module) for areas where the wiring harness may have rubbed against the chassis, causing a broken wire.

2. 2

   Unplug the electrical connector for the DEF suction line heater and inspect the pins for green or white powdery corrosion (water ingress), which creates high resistance or open circuits.

3. 3

   Using a multimeter, measure the resistance across the two pins on the heater side of the connector. A healthy heated line should show continuity (typically 3 to 15 ohms). If the multimeter reads OL (Open Loop), the heating element inside the hose is broken.

4. 4

   If the hose tests good, turn the key ON and test the harness side of the connector for voltage to ensure the ECU is sending power to the line. Check for continuity between the harness plug and the ECU pins.

1. 1

   Prep the Area

   Turn off the battery isolator switch. Clean the area around the DEF tank fittings and the DEF pump module to prevent dirt from entering the SCR system.

2. 2

   Disconnect the Line

   Unplug the electrical connector for the DEF suction line heater. Depress the release tabs on the fluid fittings and disconnect the hose from both the DEF tank and the supply pump. Note: Have a catch pan ready. Wash away any spilled DEF immediately with warm water, as it is highly corrosive to metal.

3. 3

   Remove the Old Line

   Unclip the line from its chassis routing brackets.

4. 4

   Install the New Line

   Route the new heated DEF suction line exactly as the old one was routed. Ensure it is secured tightly with zip-ties or P-clips so it does not rub against the frame or vibrate.

5. 5

   Reconnect

   Snap the fluid fittings onto the tank and pump until they click. Reconnect the electrical plug.

6. 6

   Clear Codes

   Turn the battery power back on. Use an AGCO EDT (Electronic Diagnostic Tool) or equivalent scanner to clear the 004340.05 fault code. Run a manual DEF system heater test via the diagnostic tool to verify the circuit is closed and drawing the correct amperage.