Massey Ferguson 4334.04 – Engine ECU: DEF System Pressure Sensor Voltage Low

The engine's control module has detected that the voltage signal returning from the Diesel Exhaust Fluid (DEF) pressure sensor has dropped below the normal operating range. This almost always indicates a short circuit to ground or an open circuit on the sensor's signal line.

• 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
• 7714 through 7726S

1. 1

   Check for multiple codes (e.g., SPN 3510 FMI 4) to rule out a main 5V sensor supply short.

2. 2

   Turn ignition OFF and visually inspect the DEF dosing unit/pressure sensor harness and connectors for bent, broken, pushed-out, or corroded pins.

3. 3

   Disconnect the main 120-pin ECU/ACM connector and measure resistance between the DEF pressure signal pin and chassis ground (less than 1k ohms indicates a short).

4. 4

   Turn ignition ON (engine OFF) and verify the sensor is receiving a 4.5V to 5.5V reference voltage from the ECU.

1. 1

   Disconnect power

   Turn off the equipment and disconnect the negative battery cable.

2. 2

   Repair wiring harness (if shorted)

   If diagnostic tests revealed a wiring short (resistance < 1k ohms to ground), trace the harness from the DEF Supply Module to the ECU. Locate the chafed wire, repair it using solder and marine-grade heat shrink, and secure the harness away from vibration points.

3. 3

   Remove faulty DEF Supply Module

   If the sensor is faulty internally, clean the area around the DEF Supply Module. Disconnect electrical connectors and DEF suction/pressure lines. Have a catch pan ready and clean any spilled DEF immediately with warm water.

4. 4

   Install replacement module

   Unbolt the faulty module and mount the replacement, tightening bolts to OEM torque specs. Reconnect the DEF fluid lines until they click securely, then reconnect the electrical harness.

5. 5

   Prime system and verify repair

   Reconnect the battery and clear fault codes. Start the engine and let it idle for at least 1 minute to allow the EEM4 system to prime and pressurize the DEF lines. Verify the code does not return and check for leaks.