Massey Ferguson 004332.16 – ECU: DEF System Pressure Issue

The Engine Control Unit (ECU) has detected an anomaly in the Diesel Exhaust Fluid (DEF) system's operating pressure. The pressure may be too low, too high, or failing to build as expected during system operation or priming. The DEF system relies on a specific pressure range to accurately dose fluid into the exhaust stream for the Selective Catalytic Reduction (SCR) process. This fault prevents proper operation of the emissions control system and may lead to reduced engine power.

• 5710SL
• 5711SL
• 5712SL
• 5713SL
• 7614
• 7615
• 7616
• 7618
• 7619
• 7620
• 7622
• 7624
• 7626
• 7714
• 7715
• 7715S
• 7716
• 7716S
• 7718
• 7718S
• 7719
• 7720
• 7720S
• 7722
• 7722S
• 7724
• 7724S
• 7726
• 7726S
• 4700 Series
• 5600 Series
• 8600 Series
• 8700 Series

1. 1

   Check DEF quality and level to ensure the tank is adequately filled with ISO 22241-compliant fluid (32.5% urea concentration). Perform a visual inspection for cloudiness or discoloration, and use a refractometer to verify.

2. 2

   Inspect the DEF tank, pump module, lines, and connectors for external leaks (look for white crystal formations).

3. 3

   Listen to the DEF pump when the ignition is turned on (without starting the engine); it should prime with a steady humming sound. An unusually loud, erratic, or silent pump indicates an issue.

4. 4

   Check all DEF lines and quick-connectors for obstructions, kinks, damage, or air ingress (damaged O-rings).

5. 5

   Inspect electrical wiring harnesses and connectors for the DEF pump, pressure sensor, and heating elements for corrosion, damage, or loose connections. Check for low system voltage which can also trigger electronic faults.

6. 6

   Review related fault codes (e.g., 004334.03 or 004334.04 for the pressure sensor, or codes for heaters and NOx sensors) for additional diagnostic clues.

1. 1

   Address basic issues

   Resolve any issues found during initial checks, such as refilling the DEF tank, cleaning corroded connectors, or repairing damaged wiring.

2. 2

   Replace the DEF filter

   Replace the DEF filter, as a clogged filter is a common cause of pressure issues. This should be done annually or after any fluid contamination.

3. 3

   Test the DEF dosing injector

   Perform a dosing injector test using a diagnostic scan tool. Remove the injector, place it in a measuring container, and run the test cycle. Verify a fine mist spray pattern and a collected volume of 40-55ml over a 2-minute test.

4. 4

   Test DEF system pressure

   Connect a pressure gauge to the DEF line to measure actual system pressure. This determines if the pump cannot generate pressure or if the pressure sensor is providing incorrect readings.

5. 5

   Replace the DEF pump/module

   If the pump is noisy, fails to prime, or cannot build adequate pressure during testing, replace the DEF pump or the entire DEF module.

6. 6

   Replace the DEF pressure sensor

   If the pump works correctly but pressure readings on a diagnostic tool are incorrect or implausible, replace the DEF pressure sensor.