Massey Ferguson 4346.04 – ECU: DEF Injector Supply Heater Resistance Is Low (ECU)

The Engine Control Unit (ECU) monitors the electrical resistance of the heating element integrated into the DEF (Diesel Exhaust Fluid / AdBlue) supply line. The ".04" failure mode indicator signifies that the resistance in this heater circuit is abnormally low. This typically indicates a short circuit within the heating element itself, a short to ground in the wiring harness, or a failed heater relay.

• 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
• 7714S
• 7719S

1. 1

   Visually inspect the DEF injector supply line (from the DEF pump module to the exhaust doser/injector) for pinched areas, melted insulation from exhaust heat, or chafing against the chassis.

2. 2

   Perform a resistance test by disconnecting the electrical connector for the DEF supply line heater and measuring resistance across the heater element pins. A reading near 0 ohms indicates an internal short.

3. 3

   Test the tractor-side wiring harness for continuity to ground on the power supply wire with the line disconnected to rule out a main harness short.

4. 4

   Inspect the DEF supply module heater relay for a fused or internally shorted condition.

1. 1

   Preparation

   Turn off the tractor, remove the key, and disconnect the negative battery cable. Ensure the exhaust system has completely cooled.

2. 2

   Disconnect Electricals

   Unplug the electrical connector for the DEF supply line heater.

3. 3

   Remove Fluid Fittings

   Disconnect the quick-connect fluid fittings at the DEF pump module and the DEF injector. Note: Have a clean catch pan ready, as residual DEF will spill. Do not let DEF contact electrical connectors, as it is highly corrosive.

4. 4

   Remove the Line

   Unclip the heated line from its routing brackets and remove it from the tractor.

5. 5

   Install the New Line

   Route the new DEF injector supply line exactly as the original was routed. Ensure it is secured in its clips and kept safely away from sharp edges and hot exhaust components.

6. 6

   Reconnect

   Snap the fluid quick-connects into place until they click. Plug in the heater electrical connector.

7. 7

   Clear Codes and Prime

   Reconnect the battery. Use a compatible diagnostic scan tool (such as AGCO EDT) to clear the 004346.04 fault code. Run a DEF system prime/leak test via the scan tool to ensure the system pressurizes without leaks.