Case IH 19142 (DTC 4DCA) - ECU – Engine Control Module (ECM) / Dosing Control Unit (DCU): DEF/AdBlue quality sensor temperature failure

The DEF quality sensor measures both the urea concentration and the fluid temperature, while the DEF level sensor also has a temperature reading. This fault code triggers a rationality error when the temperature reading from the DEF quality sensor significantly disagrees with the temperature reading from the DEF level sensor.

• MAXXUM T4E
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Magnum
• Steiger
• Optum
• Farmall

1. 1

   Perform a cold soak temperature comparison using a diagnostic scanner. After sitting overnight, both the DEF Quality Sensor Temperature and DEF Level Sensor Temperature should closely match the ambient air temperature. The sensor showing an erratic or out-of-range value is the failed component.

2. 2

   Inspect the wiring harness and connectors at the top of the DEF tank (DEF header) for green/white powdery corrosion caused by ammonia gas leaks.

3. 3

   Check for low battery voltage codes (such as SPN 168, FMI 1), as low voltage is the most common cause of phantom DEF sensor codes on Case IH equipment.

4. 4

   Ensure the DEF tank is filled with clean, uncontaminated Diesel Exhaust Fluid.

1. 1

   Park the machine on a level surface, turn off the engine, and disconnect the battery to prevent electrical shorts or accidental DEF dosing pump activation.

2. 2

   Locate the DEF header unit, which is mounted on the top of the DEF tank.

3. 3

   Thoroughly clean the top of the DEF tank around the sensor mounting flange to prevent dirt, debris, or rust from falling into the DEF fluid during removal.

4. 4

   Disconnect the electrical connector from the DEF quality sensor.

   If the connector is corroded, it must be cut and a new pigtail spliced in.

5. 5

   Remove the mounting bolts/screws securing the DEF header/quality sensor assembly to the tank.

6. 6

   Carefully pull the sensor assembly straight up and out of the tank.

7. 7

   Install the new DEF quality sensor assembly, ensuring the rubber gasket/O-ring is properly seated to prevent ammonia gas leaks.

8. 8

   Torque the mounting hardware to OEM specifications.

9. 9

   Reconnect the electrical harness and the battery.

10. 10

    Turn the key to the ON position. Connect the diagnostic tool, clear the 19142 (4DCA) fault code, and verify that the temperature readings now match and the engine derate/warning lights are extinguished.