Massey Ferguson 520227.31 – Engine Control Unit (ECU) / AGCO SISU POWER EEM4: ECU internal fault 0120 / Diagnostic fault check to report the error in overvoltage monitoring / Module multiple supply

This code indicates a critical internal hardware or software failure within the engine controller. Specifically, the module's internal overvoltage monitoring circuit has detected a fault or failed its self-diagnostic check.

• 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
• 6700 S
• 7600
• 7700 S
• 8600
• 8700
• Tier 3 AGCO Power engines
• Tier 4 Final AGCO Power engines
• D49FSR engines

1. 1

   Check system voltage using a multimeter to verify battery voltage and alternator output, ensuring the alternator is not overcharging the system (which can trigger false overvoltage faults).

2. 2

   Inspect the 154-pin or 192-pin wiring harness connectors at the EEM4 ECU for corrosion, water intrusion, or shorted wires that could send unregulated voltage to the module.

3. 3

   Clear the code using the AGCO Electronic Diagnostic Tool (EDT) or WinEEM4 software and retest. If the code returns immediately upon key-on or cranking, the ECU has suffered a hard internal failure.

1. 1

   Disconnect Power

   Disconnect the negative battery cable to prevent electrical arcing.

2. 2

   Remove the ECU

   Locate the EEM4 ECU (typically mounted on the side of the engine block). Carefully release the locking levers on the main wiring harness connectors and unplug them. Unbolt the ECU from its mounting bracket.

3. 3

   Install the New ECU

   Bolt the replacement ECU into place and securely reconnect the wiring harnesses, ensuring the locking levers are fully seated.

4. 4

   Programming

   Use the AGCO EDT (Electronic Diagnostic Tool) and WinEEM4 software to perform End-Of-Line (EOL) programming. This flashes the correct engine specification, injector trim codes, and tractor configuration to the new module. The tractor will not run correctly (or at all) without this calibration.