Massey Ferguson 521008 – Engine ECU (EEM4): SCR system ERROR: DEF pressure reduction failure

The system is unable to properly reduce or bleed off the Diesel Exhaust Fluid (DEF) pressure within the Bosch DNOX2.2 dosing system.

• 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
• 4700 series
• 5600 series
• 5700 series
• 6600 series
• 6700 series
• 7600 series
• MF7600
• 7700 series
• 8600 series
• 8700 series
• 8S series
• Gleaner combines

1. 1

   Check for a 'Dry Pump' condition if the machine has been sitting for a long standstill period (pump membrane can dry out and lose suction)

2. 2

   Inspect the DEF tank draw tube and suction filter for a broken tab that allows the filter to move and block fluid flow

3. 3

   Check the inline AdBlue/DEF inlet filter and the main DEF filter for clogs, crystallization, or contamination

4. 4

   Inspect the wiring harness connecting the Engine ECU to the DEF Supply Module (pump) for chafing, breaks, or shorts

5. 5

   Verify DEF quality to ensure it is not contaminated with diesel, oil, or water

1. 1

   Prime/Moisturize the Pump

   If the machine has been in storage, manually moisturize the pump with fresh DEF. Once the membrane is wet, the supply module will often recover its suction and operate normally.

2. 2

   Replace Filters

   Replace the AdBlue inlet filter and the main DEF filter element. This is the most common mechanical fix for flow/pressure restrictions.

3. 3

   Secure/Replace the Draw Tube Filter

   If the draw tube filter inside the tank is broken or floating loose, replace the filter or the DEF tank head unit assembly.

4. 4

   Replace the Supply Module

   If the wiring is intact, the filters are new, and the system still cannot reduce or build pressure, the Bosch DNOX2.2 Supply Module (DEF pump) has failed internally and must be replaced.

5. 5

   System Test

   After repairs, use a diagnostic service tool to clear the EEM4 fault codes. Perform an 'Aftertreatment SCR System Dosing Test' to force the pump to run at a predetermined speed and verify that pressure stabilizes correctly.