Massey Ferguson E521008.01 – Engine ECU (EEM4): DEF Pressure Issue (ECU) / SCR system ERROR: DEF pressure build up failure

The engine's monitoring system has detected that the Selective Catalytic Reduction (SCR) system cannot be pressurized. The system is failing to build the required Diesel Exhaust Fluid (DEF) pressure to dose the exhaust stream properly.

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624
• 4707
• 4708
• 4709
• 4710
• 5710 SL
• 5711 SL
• 5712 SL
• 5713 SL
• 7714 through 7726S

1. 1

   Check DEF tank level to ensure it is not too low

2. 2

   Inspect the DEF tank cap and breather for defective ventilation, which can create a vacuum and prevent the pump from drawing fluid

3. 3

   Inspect the entire SCR system (supply and return lines) for visible leaks, rub points, or nicked O-rings that could cause air ingress

4. 4

   Check the DEF supply module inlet connector and the DEF tank outlet connector for blockages or crystallized DEF

5. 5

   Ensure the DEF supply module inlet hose is not kinked, blocked, or leaking

6. 6

   Verify the wiring harness to the DEF supply module is intact and not defective

7. 7

   If possible, test the system operation with a known-good DEF supply module to isolate if the current pump is internally defective

1. 1

   Clear the Log

   Connect your diagnostic tool, save the error log, and then erase it.

2. 2

   Cycle the ECU

   Restart the ECU (key cycle) and perform a test drive/operation cycle. If the fault is active, the engine power will eventually derate.

3. 3

   Perform Visual & Physical Inspections

   If the fault returns, perform the physical diagnostic checks listed above (ventilation, line kinks, leaks, and blockages).

4. 4

   Service the Filter

   Clean the DEF tank neck and replace the DEF supply module filter/strainer, as a clogged filter will starve the pump and prevent pressure buildup.

5. 5

   Replace the Pump

   If all lines, connections, wiring, and ventilation are clear and leak-free, the DEF supply module (pump) has failed internally and must be replaced.

6. 6

   Final Verification

   Clear the codes again and run the tractor under load to ensure the SCR system pressurizes and the code does not return.