Massey Ferguson 521002.05 – Engine ECU (EEM4 / Aftertreatment Control Module): Aftertreatment Diesel Exhaust Fluid (DEF) Return Valve / Reverse Flow Solenoid - Current Below Normal or Open Circuit

The Engine Control Unit (ECU) has detected that the electrical current draw from the DEF reverse flow solenoid is below the minimum target range, indicating a broken wire, a disconnected plug, or an internal open circuit inside the solenoid itself. (Note: 521002.05 is a John Deere code; the equivalent Massey Ferguson code for this DEF issue is E4376.05).

• 7616
• 5612
• 7622
• Interim Tier 4 (2012-2015)
• 7614
• 5611
• 7615
• 5610
• 5613
• 7620
• 5609
• 7618
• 5608
• 7619
• 7626
• 7624

1. 1

   Visual Inspection: Inspect the wiring harness routing from the Engine ECU to the DEF Supply Module (pump assembly) for chafing, breaks, or melted sections.

2. 2

   Connector Check: Disconnect the harness at the DEF return valve/pump assembly. Check for "greened" (corroded) pins, moisture intrusion, or pushed-out terminals.

3. 3

   Continuity Test: Use a multimeter to verify continuity on the power and ground circuits between the ECU and the DEF return valve connector.

4. 4

   Component Resistance: Measure the resistance across the pins of the DEF reverse flow solenoid itself. If it reads as an open circuit (infinite resistance/OL), the solenoid has failed internally.

1. 1

   Power Down

   Turn the ignition off and wait for at least 60 seconds to allow the ECU to save data and the aftertreatment system to complete its purge cycle.

2. 2

   Isolate the Fault

   Based on the diagnostic checks, determine if the fault is in the wiring harness or the valve itself.

3. 3

   Wiring Repair

   If a broken wire or corroded connector is found, splice in a new section of wire using weather-sealed connectors or replace the damaged pigtail connector.

4. 4

   Valve Replacement

   If the solenoid tests open, replace the DEF Return Valve. Note: On many Bosch DEF supply modules used by AGCO/Massey Ferguson, the return valve is integrated into the DEF pump assembly and cannot be serviced separately; the entire DEF pump module must be replaced.

5. 5

   Reassembly & Testing

   Reconnect all harnesses. Turn the ignition on and use a diagnostic service tool to clear the fault codes. Run an aftertreatment system test or perform a test drive to ensure the ECU powerstage is re-enabled and the code does not return.