Massey Ferguson 4344.02 – Engine ECU: DEF Unit Internal Temperature Sensor Issue / DEF supply module heater temperature signal in invalid range.

The Engine ECU is receiving an erratic, implausible, or invalid temperature signal from the heater temperature sensor located inside the DEF (Diesel Exhaust Fluid) supply module. Because the sensor is integrated into the pump, a failure of this sensor usually means the entire module is compromised.

• 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
• 8650
• 8670

1. 1

   Perform a system reset by turning the ignition off for a minimum of 60 seconds to allow the ECU to power down and the DEF system to complete its purge cycle. Turn it back on to see if the code remains active.

2. 2

   Inspect the wiring harness and connectors between the Engine ECU and the DEF supply module for chafing, corrosion, or loose pins that could cause an invalid signal.

3. 3

   Check for related active codes on the same circuit (e.g., SPN 4344 FMI 3, 4, or 5), which would indicate a hard short to ground, short to high source, or an open circuit in the wiring harness.

4. 4

   Use a diagnostic service tool (like WinEEM4) to monitor the DEF supply module heater temperature signal. If the wiring is intact but the signal remains invalid or unresponsive, the internal sensor has failed.

1. 1

   Power Down

   Turn off the ignition and wait at least 60 seconds for the DEF pump to purge fluid back into the tank.

2. 2

   Disconnect Power

   Disconnect the battery or the EEM4 controller main connectors before working on the electrical system to prevent voltage spikes.

3. 3

   Clean the Area

   Clean the area around the DEF supply module to prevent dirt from entering the DEF lines. (Note: If using a high-pressure washer, cover the ECU and electrical connectors).

4. 4

   Disconnect Lines

   Disconnect the electrical harness from the DEF supply module. Carefully disconnect the DEF fluid lines (suction, pressure, and backflow). Cap the lines immediately to prevent contamination.

5. 5

   Remove Module

   Unbolt the defective DEF supply module from its mounting bracket and remove it.

6. 6

   Install New Module

   Mount the new DEF supply module and secure the bolts.

7. 7

   Reconnect

   Remove the caps and reconnect the DEF fluid lines, ensuring they click securely into place. Reconnect the electrical harness.

8. 8

   Restore Power & Clear Codes

   Reconnect the battery. Use a diagnostic tool to clear the error log and run a system test to verify the new pump's temperature signal and dosing operation.