Massey Ferguson 4334.03 – ECU: DEF System Pressure Sensor Voltage High (ECU)

The engine management system has detected that the signal voltage from the Diesel Exhaust Fluid (DEF) pressure sensor is higher than the expected normal range. This typically indicates a short circuit to a high voltage source (e.g., 12V) or an open circuit in the sensor's wiring harness.

• 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

   Inspect the wiring harness running from the ECU to the DEF supply module (pump) for chafing, melting, or broken wires.

2. 2

   Disconnect the DEF supply module connector and check for corrosion, bent pins, or moisture intrusion.

3. 3

   Test the DEF pressure sensor circuit for an open circuit or a short to a high voltage source (+12V or +5V). Note: Pin 2 is +5V power supply, Pin 3 is pressure sensor signal, and Pin 4 is sensor ground.

4. 4

   Temporarily connect a known-good DEF supply module to the harness to see if the fault clears, which isolates the issue to an internal short or defect in the original module.

1. 1

   Disconnect Power

   Turn off the ignition and disconnect the battery to prevent electrical spikes.

2. 2

   Repair Wiring

   If the diagnostic checks revealed a short to power or an open wire in the harness, splice and repair the damaged section using weather-sealed connectors, or replace the affected harness section.

3. 3

   Replace the DEF Supply Module

   If the sensor has failed internally, the module must be replaced. Relieve any residual pressure in the DEF lines. Disconnect the electrical connector and the DEF fluid lines from the supply module. Unbolt the module from its mounting bracket and install the new unit. Reconnect the fluid lines and electrical connector.

4. 4

   System Prime and Code Clearing

   Reconnect the battery. Turn the ignition on. Use a compatible diagnostic service tool (such as AGCO EDT or JPRO) to clear the 004334.03 fault code. Start the engine and allow the exhaust to reach operating temperature (approx. 120°C / 250°F) so the EEM4 system can command the pump to pressurize and prime the lines. Verify the code does not return.