Case IH 19166 – Engine Control Module (ECM) or Denoxtronic Control Unit (DCU) / SCR Controller: DEF/AdBlue quality sensor internal failure (Temperature sensor circuit short to ground)

The sensor responsible for measuring the concentration/quality and temperature of the Diesel Exhaust Fluid (DEF) has detected a short to ground in its internal temperature circuit. A known issue is that ammonia gas from the DEF tank can seep into the sensor housing, corroding the internal circuit board and causing electrical shorts.

• Tier 4b
• Steiger
• Quadtrac
• Magnum
• Optum
• Puma
• Maxxum
• Farmall C series
• 240 Series Axial-Flow Combines
• 7240
• 8240
• 9240

1. 1

   Inspect the wiring harness leading to the DEF quality sensor for chafing, cuts, or physical damage causing a short to ground.

2. 2

   Disconnect the DEF quality sensor connector and inspect for corrosion from ammonia gas intrusion.

3. 3

   Unplug the DEF quality sensor to isolate it; if the CAN bus comes back online or the fault changes to an open circuit, the internal short is confirmed.

4. 4

   Ensure the DEF tank vent lines are not blocked by crystallized DEF.

1. 1

   Power Down

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

2. 2

   Locate the Sensor

   Locate the DEF header assembly, which sits on the very top of the DEF tank. The DEF quality sensor is integrated into this header unit.

3. 3

   Disconnect Lines

   Carefully disconnect the electrical connector and the DEF fluid lines attached to the header.

4. 4

   Remove the Header

   Remove the mounting bolts or the retaining ring securing the DEF header to the tank.

5. 5

   Extract the Unit

   Carefully lift the old DEF header/quality sensor assembly out of the tank.

6. 6

   Install the New Part

   Insert the new DEF header assembly into the tank, ensuring the seal/gasket is seated correctly to prevent future ammonia gas leaks.

7. 7

   Reassemble

   Fasten the mounting bolts/ring, and reconnect the DEF fluid lines and the electrical connector.

8. 8

   Clear Codes

   Reconnect the battery. Use the Case IH AFS Pro 700 display or the Electronic Service Tool (EST) to clear the latched fault codes and reset the system.