Massey Ferguson E4346.03 – ECU: DEF Injector Supply Pipe Heater Resistance Is High

The system has detected that the electrical resistance in the heating element of the DEF (Diesel Exhaust Fluid) supply line is higher than the specified normal range. This typically indicates an open circuit, a broken internal heating wire, or a severely corroded electrical connector. The heater is integrated into the line to thaw DEF fluid in cold weather; if the heater fails, the system cannot guarantee fluid delivery in freezing conditions, which will eventually trigger an engine derate.

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

1. 1

   Visually inspect the electrical connectors that supply power to the DEF line heater for road salt corrosion, moisture, or loose pins.

2. 2

   Perform a resistance test (Ohms) across the heater pins on the DEF supply line. A healthy line should show 3 to 5 ohms; 'OL' or excessively high resistance indicates a broken internal heating element.

3. 3

   Perform a voltage test on the harness side of the connector by commanding the DEF heater relay on to verify a full 12V is being supplied, ruling out the ECU or relay.

1. 1

   Depressurize the System

   Turn off the ignition and wait for the DEF system to complete its automatic purge cycle. Do not disconnect lines while the system is pressurized.

2. 2

   Cool Down

   Ensure the engine and exhaust components (where the DEF injector is located) are completely cool to avoid burns.

3. 3

   Disconnect Electricals

   Unplug the electrical connector for the DEF supply line heater.

4. 4

   Disconnect Fluid Lines

   Disconnect the DEF fluid quick-connect fittings at the DEF supply module (pump) and at the DEF doser/injector. Have a rag ready to catch minor fluid drips. Clean any spilled DEF with warm water to prevent corrosion.

5. 5

   Remove the Line

   Unclip the DEF line assembly from its retaining clips along the tractor's frame rail and remove it.

6. 6

   Install the New Line

   Route the new heated DEF supply line exactly as the old one was routed. Secure it in all factory clips to prevent chafing or proximity to extreme exhaust heat.

7. 7

   Reconnect

   Snap the fluid fittings back into place (ensure they click securely) and plug in the electrical connector.

8. 8

   Clear Codes

   Use an AGCO diagnostic tool (like WinEEM4) to clear the E4346.03 fault code from the ECU and run a system test to verify the repair.