Encountering SPN 1485 FMI 03 on an AGCO machine (such as Fendt, Massey Ferguson, or Valtra equipped with AGCO Power EEM4 engines) indicates an electrical malfunction in the SCR/DEF DNOX2 Supply Module (SM).
Fault Code Overview
- SPN (Suspect Parameter Number): 1485 – Engine ECU Main Relay / Supply Module Main Relay
- FMI (Failure Mode Indicator): 03 – Voltage Above Normal or Shorted to High Source
- System Affected: DNOX2 DEF/AdBlue Supply Module (SM) & Engine Management System (EEM4)
- CAN Bus Status: Broadcast on the engine CAN network; permanent trouble code logged into the DNOX2 EEPROM.
What Causes SPN 1485 FMI 03?
The AGCO DNOX2 supply module contains internal semiconductor main relays designed to manage system power and the critical post-shutdown purge sequence (after-run cycle).
When the operator turns off the ignition key:
- The DNOX2 system performs automated after-run tasks, such as draining DEF lines back into the tank to prevent freezing and crystallization.
- Once the after-run cycle finishes, the internal software commands the semiconductor relays to shut off.
- If an internal relay fails to shut off or detects a voltage higher than standard operating thresholds, the ECU triggers SPN 1485 FMI 03 (No shut-off of main relay / shorted high).
Note: These semiconductor relays are permanently sealed inside the DNOX2 Supply Module and cannot be serviced or replaced independently.
Diagnostic & Repair Workflow
Required Tools
- AGCO EDT (Electronic Diagnostic Tool) or compatible diagnostic software
- AGCO 2×4 CANUSB Diagnostic Interface
- Digital Multimeter (DMM)
Step-by-Step Diagnostic Procedure
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Observe Safety Precautions
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Before working on the SCR system, review standard DNOX2 General Instructions and Precautions. Ensure the machine has been keyed off long enough for the after-run cycle to attempt completion.
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Verify Power and Ground Supply
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Inspect the external wiring harness connecting to the DNOX2 supply module.
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Check for back-fed 12V/24V power, short circuits to battery positive ($B+$), or ground circuit deterioration that could prevent normal module power-down.
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Check Diagnostic Status in AGCO EDT
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Connect the CANUSB interface to the diagnostic port.
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Clear active faults and run an automated after-run functional test to see if the relay latches open continuously.
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Isolate the Fault (Component Swap Test)
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If wiring integrity passes inspection and the relay remains locked in the active position, connect a known-good test Supply Module.
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Power cycle the machine. If SPN 1485 FMI 03 clears and does not return during the after-run sequence, the internal semiconductor relay in the original module has failed.
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Resolution
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Replace the complete DNOX2 Supply Module (SM) assembly.
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Calibrate/configure the new module using the AGCO EDT software and perform a complete key-cycle test to ensure fault-free operation.
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More AGCO machine repair case,please refer to AGCO Machine Repair
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