Case IH F-519044-04 - ECU – Engine Control Module (ECM) or Dosing Control Unit (DCU) / SCR Control Module: DEF/AdBlue quality sensor internal failure (Temperature sensor circuit short to ground)

The DEF quality sensor is an integrated component that measures the urea concentration, fluid level, and fluid temperature to ensure the Selective Catalytic Reduction (SCR) system functions properly. The "FMI 04" designation indicates a "Voltage Below Normal" or "Short to Ground" condition. Because the temperature sensor is built directly into the DEF quality sensor assembly, this code typically indicates an internal failure of the sensor itself.

• MAGNUM AFS Connect
• 240 Series Axial-Flow Combines
• Magnum series (e.g., Magnum 380, CVT models)
• Steiger series
• Farmall
• Patriot series (e.g., 4440)

1. 1

   Visual Inspection: Inspect the wiring harness leading to the DEF tank head unit. Look for chafed wires, melted insulation, or physical damage that could cause a short to ground.

2. 2

   Connector Check: Disconnect the DEF quality sensor electrical connector. Check for corrosion, moisture, or pushed-back pins.

3. 3

   Circuit Testing: Use a multimeter to verify that the sensor is receiving proper voltage and ground from the ECM/DCU. Test the signal wire for continuity and ensure it is not shorted to the chassis ground.

4. 4

   Fluid Quality Check: Ensure the DEF tank is not filled with contaminated fluid or crystallized DEF, which can sometimes cause erratic sensor readings or block the sensor face.

1. 1

   Prep the Machine

   Turn off the machine and disconnect the battery. Clean the area around the top of the DEF tank to prevent dirt from falling into the tank.

2. 2

   Drain Fluid

   Drain the DEF tank or siphon the fluid so the level is below the sensor mounting flange.

3. 3

   Disconnect Lines

   Carefully disconnect the electrical connector from the DEF head unit. Disconnect the DEF supply and return lines, as well as the engine coolant heating lines (if equipped). Cap the lines to prevent contamination.

4. 4

   Remove the Sensor

   Unscrew the mounting ring or unbolt the flange securing the DEF head unit to the tank. Carefully pull the old sensor assembly straight up and out of the tank.

5. 5

   Install the New Sensor

   Insert the new DEF quality sensor into the tank using a new mounting seal/O-ring. Secure the flange/mounting ring to the specified torque.

6. 6

   Reconnect

   Reconnect the DEF lines, coolant lines, and the electrical connector.

7. 7

   Refill

   Refill the tank with fresh, clean Diesel Exhaust Fluid (32.5% urea concentration).

8. 8

   Clear Codes

   Reconnect the battery. You will likely need to use the Case IH Electronic Service Tool (EST) to clear the latched fault codes, reset the system, and run a reductant fluid quality test to take the engine out of derate mode.