Case IH 19134 – Engine Control Module (ECM) or Dosing Control Unit (DCU) / SCR Controller: DEF/AdBlue Quality sensor detects Air

The DEF quality sensor is reading air instead of liquid. This condition is typically caused by an empty DEF tank, a broken pickup tube, air trapped in the sensor housing, or a failed sensor circuit board due to ammonia gas corrosion.

• Tier 4b
• Case IH Puma
• Case IH Magnum
• Case IH Optum
• Case IH Steiger
• Case IH Quadtrac
• Quadtrac 500 Tier 4B

1. 1

   Verify DEF Fluid Level: Ensure the DEF tank is not empty or critically low. If the fluid drops below the sensor pickup, it will naturally read air.

2. 2

   Inspect the DEF Tank Header: Check the DEF tank header unit (where the quality sensor is housed) for physical damage, cracks, or a broken pickup tube that could be drawing in air.

3. 3

   Check for Trapped Air / Leaks: Inspect the DEF suction lines between the tank and the supply module for pinhole leaks that could introduce air into the system.

4. 4

   Inspect Wiring and Connectors: Disconnect the DEF quality sensor electrical connector. Check for green corrosion (a sign of ammonia exposure) or moisture on the pins.

5. 5

   Check for Software Updates: Check with a Case IH dealer to see if a software flash is available to bypass the sensor, relying instead on the post-treatment NOx sensor.

1. 1

   Refill and Prime

   Fill the DEF tank with fresh, high-quality AdBlue/DEF to ensure the sensor is fully submerged. Clear the fault code using a diagnostic scan tool (like the AFS Pro display) and cycle the key/run the engine to prime the DEF dosing system and purge any trapped air.

2. 2

   Clean Connections

   If the code returns, disconnect the sensor harness. Clean the female electrical connector with contact cleaner and apply dielectric grease. Reconnect and retest.

3. 3

   Replace the DEF Tank Header Assembly

   If the tank is full, the wiring is intact, and the code persists, the internal circuit board of the DEF quality sensor has likely failed due to ammonia corrosion. The sensor is integrated into the DEF tank header assembly.

4. 4

   Removal/Installation

   Disconnect the battery. Disconnect the coolant lines (used for thawing DEF), DEF suction/return lines, and electrical connectors from the top of the DEF tank header. Unbolt the header ring and pull the entire header/sensor assembly out of the tank. Install the new assembly, reconnect all lines, and clear the codes.