Massey Ferguson 4346.05 – Engine Control Unit (ECU): DEF Injector Supply Heater Open Circuit (ECU)
Issue description
This code indicates that the system has detected a break (open circuit) in the electrical circuit for the Diesel Exhaust Fluid (DEF) injector supply line heater. DEF freezes at 12°F (-11°C), so the lines are equipped with heating elements to thaw the fluid and maintain flow. An open circuit means electrical current cannot flow through the heater, usually due to a burned-out heating element inside the line, a broken wire, or a disconnected plug.
Applies to these machines
81 machines- 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
- 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
Check the cause
Verify the Code: Enter the tractor's diagnostic mode via the control panel to confirm 004346.05 is currently active.
Visual Inspection: Locate the DEF supply line running from the DEF pump to the DEF injector on the exhaust/SCR unit. Inspect the electrical pigtail connector for the heater. Look for disconnected plugs, corroded pins, or physical damage to the wiring harness.
Resistance Test (Heater Element): Disconnect the DEF supply line heater connector. Use a digital multimeter to measure the resistance (Ohms) across the pins on the heater side. If the multimeter reads 'OL' (Open Loop) or infinite resistance, the heating element inside the line has failed and the line must be replaced.
Harness Continuity Test: If the heater element shows normal resistance, check the tractor-side wiring harness for continuity back to the ECU to rule out a broken wire in the main harness.
Repair steps
Park the tractor on a level surface, shut down the engine, set the parking brake, and disconnect the battery.
Clean the area around the DEF supply line fittings with warm water.
DEF crystallizes when exposed to air, and warm water dissolves it safely.
Disconnect the electrical pigtail connector for the DEF supply line heater.
Disconnect the fluid fittings at both ends of the supply line (at the pump/tank and at the injector).
*Note: Be prepared to catch a small amount of spilled DEF.*
Remove the faulty heated line from its routing clips.
Route the new DEF Injector Supply Heated Line into place.
Snap the fluid fittings onto the injector and pump connections until they click securely.
Reconnect the electrical pigtail to the main harness.
Reconnect the battery, turn the key on, and use the dashboard diagnostic mode or a service tool to clear the fault codes.
Run the engine to ensure the code does not return and there are no fluid leaks.
Parts you might need
(1)DEF Injector Supply Line (Heated) / DEF Heated Pressure Line Hose
Specific AGCO part numbers vary heavily based on the exact chassis length and series. The replacement part is typically sold as a complete assembly containing the fluid hose, the integrated heating element, and the electrical pigtail.
Get help to fix this fault by requesting a quote
