Case IH 19166 (DTC 794E) - ECU – Engine Control Unit (ECU): DEF/AdBlue quality sensor internal failure

The system has detected a short circuit (often a short to battery or short to ground) in the temperature sensor circuit that is located internally within the DEF/AdBlue quality sensor.

• MAXXUM T4E
• Axial-Flow Combines (5130 and 240 Series)
• Steiger / Quadtrac Tractors (Quadtrac 500)

1. 1

   Inspect the DEF quality sensor wire harness and the female electrical connector at the DEF tank header for frayed wires, chafing, or a short to the battery/ground.

2. 2

   Inspect the sensor housing for signs of ammonia corrosion. Ammonia gas can seep into the top of the sensor box and corrode the internal electronic circuit board.

3. 3

   Verify the sensor is communicating properly on the CAN bus, as the ECU relies on this network to read the temperature and urea concentration data.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the battery to prevent electrical spikes.

2. 2

   Locate the Sensor

   Locate the DEF tank. The DEF quality sensor is integrated into the DEF header unit/delivery system, positioned on the very top of the DEF tank.

3. 3

   Clean the Area

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

4. 4

   Disconnect

   Unplug the electrical connector from the DEF quality sensor.

5. 5

   Remove the Sensor

   Unbolt the DEF header/quality sensor assembly and carefully pull it out of the tank.

6. 6

   Install the New Part

   Insert the replacement DEF quality sensor into the tank, ensuring the gasket/seal is properly seated to prevent future ammonia gas leaks. Secure the mounting bolts.

7. 7

   Reconnect

   Plug the electrical connector back into the sensor.

8. 8

   Clear Codes

   Reconnect the battery, turn the key on, and use a diagnostic scan tool to clear the 19166 (794E) fault code from the ECU.