Massey Ferguson 521007.31 – Engine Control Unit (ECU): DEF Pressure Issue (ECU)

The Aftertreatment system is unable to build, maintain, or read the correct Diesel Exhaust Fluid (DEF) pressure required for the dosing valve to inject fluid into the Selective Catalytic Reduction (SCR) system. This is typically caused by a failing DEF pump, a clogged DEF filter, blocked lines, or a faulty pressure sensor within the 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

1. 1

   Verify the DEF tank has adequate fluid. Sample the fluid from the mid-tank and test the concentration using a refractometer or test strips to rule out contamination or dilution.

2. 2

   Look for white crust (crystallization) near the doser valve, pump, and heated lines, which indicates a leak or chronic under-dosing.

3. 3

   Inspect the DEF tank vent to ensure it is clean and free of debris. Warning: Do not blow compressed air through the vent line into the tank, as this will introduce debris into the DEF tank. Check all DEF suction and pressure lines for kinks or blockages.

4. 4

   Check the DEF pump fuse and inspect the wiring harness for the pump and pressure sensor for chafing, proper voltage, and ground.

5. 5

   Using a diagnostic tool, run a DEF pump priming test followed by a DEF doser test. Monitor the live pressure data (the system should typically build between 100-140 psi). If the system builds pressure successfully during the test, the pump is not the issue, and the supply side (tank/lines) must be investigated.

1. 1

   Preparation

   Ensure the work area and all tools are extremely clean. The DEF system is highly sensitive to dirt and contamination.

2. 2

   Depressurize the System

   Turn off the ignition key and wait for the DEF system to complete its automatic purge cycle (which pulls fluid back into the tank to prevent freezing) before disconnecting any lines.

3. 3

   Filter Maintenance

   If the pump runs but struggles to build pressure, remove the DEF pump housing cover and replace the main DEF filter.

4. 4

   Component Replacement

   If the pump fails to prime, has internal electrical faults, or the integrated pressure sensor has failed (and wiring has been verified), replace the DEF Pump Assembly.

5. 5

   Reassembly & Verification

   Reconnect the coolant lines, DEF fluid connectors, and electrical harnesses to the new pump.

6. 6

   Clear and Test

   Clear the 521007.31 fault code using a diagnostic tool. Run a forced system test or parked regeneration to verify that the pump builds adequate pressure and the code does not return.