Massey Ferguson 4332.18 – Engine ECU (AGCO SISU POWER EEM4): SCR system ERROR: DEF dosing pressure below normal

The Selective Catalytic Reduction (SCR) system is unable to build or maintain the required pressure to properly inject Diesel Exhaust Fluid (DEF) into the exhaust stream.

• 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
• 8660
• 8670
• 8680
• 8690
• 8727
• 8730
• 8732
• 8737

1. 1

   Perform a system reset by turning the ignition off for a minimum of 60 seconds to allow the system to complete its purge cycle, then turn it back on to see if the code clears

2. 2

   Inspect all DEF suction and pressure lines for kinks, leaks, or blockages

3. 3

   Verify the DEF tank has adequate fluid and that the DEF is not contaminated or crystallized

4. 4

   Check the DEF pump filter for restrictions or heavy crystallization

5. 5

   Inspect the wiring harness and connectors going to the DEF pressure sensor and the DEF dosing pump for open circuits, shorts to ground, or corrosion

6. 6

   Use the WinEEM4 service tool to run a Pressure drop test (SPN 4332 FMI 14) and monitor the DEF pressure sensor voltage to verify if the pump is attempting to build pressure

1. 1

   Depressurize and Purge

   Ensure the tractor has been turned off for at least 60 seconds so the DEF system can purge fluid back into the tank and depressurize.

2. 2

   Replace the DEF Filter

   If the filter has not been serviced recently, remove the filter housing cap on the DEF supply module, extract the old filter element, clean any crystallized urea from the housing with warm water, and install a new OEM filter.

3. 3

   Clear Lines

   If blockages are found in the DEF lines during the diagnostic phase, flush them with warm distilled water or replace the affected hoses.

4. 4

   Replace the Dosing Module

   If the filter is clean, lines are clear, and electrical signals are verified but pressure remains low, the DEF dosing pump/injector module has failed internally. Disconnect the electrical harness and DEF lines from the module, unbolt it from its mounting bracket, and install the replacement unit.

5. 5

   Clear Codes and Test

   Connect the diagnostic tool, clear the 004332.18 fault code, and run a forced DEF dosing test to confirm the system now builds and holds the correct pressure.