Massey Ferguson 004332.00 – ECU: DEF System Pressure High

The Engine Control Unit (ECU) has detected that the pressure within the Diesel Exhaust Fluid (DEF) system is higher than the acceptable, calibrated range. This indicates a blockage, restriction, or malfunction in the components responsible for regulating and circulating the DEF. Abnormally high pressure can lead to incorrect dosing, potential damage to system components, and will likely trigger an engine power derate or limp mode to prevent emissions violations and protect the aftertreatment system.

• 4707
• 4708
• 4709
• 4710
• 5608
• 5609
• 5610
• 5611
• 5612
• 5613
• 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

1. 1

   Verify DEF quality in the tank is clean, free of contamination (such as diesel fuel, oil, or water), and meets ISO 22241 standards.

2. 2

   Visually inspect the DEF injector/doser nozzle, DEF lines, and tank filler neck for white, crusty crystal deposits indicating dried DEF.

3. 3

   Inspect all DEF lines, particularly the return line from the pump module back to the tank, for any kinks, collapses, or physical damage that could restrict flow.

4. 4

   Listen to the DEF pump during the system's priming and purging cycles (at key-on and key-off) for unusually loud, grinding, or silent operation.

5. 5

   Review the system for any other active fault codes related to the DEF pressure sensor, return valve, or pump control circuit.

1. 1

   Address crystallization

   If significant crystallization is found, carefully clean the affected components. Clean the DEF injector nozzle with deionized water. Do not use high-pressure air to blow out lines unless it is certified oil-free, as this can introduce contaminants.

2. 2

   Test the return line

   Disconnect the return line at the pump module and check for blockages. Inspect the return orifice or check valve in the fitting, as a clogged return line is a primary cause of pressure building up in the system.

3. 3

   Diagnose the DEF pressure sensor

   Compare the sensor's reading on a diagnostic tool to a known-good manual pressure gauge teed into the system. A faulty sensor reading inaccurately low can cause the ECU to over-pressurize the system.

4. 4

   Inspect and replace DEF supply module

   If the return lines are clear and the sensor is accurate, the internal pressure regulating or return valve may be stuck closed. Replace the entire DEF pump/supply module.