Case IH 19559 (DTC F18F) - ECU – DCU (Dosing Control Unit): DEF/AdBlue level too low warning is active - Stage 1

This is a Stage 1 warning indicating that the Diesel Exhaust Fluid (DEF) / AdBlue level in the tank has dropped below the first programmed warning threshold. If ignored, the system will eventually trigger a Stage 2 warning (Code 19568) and induce an engine power derate to comply with emissions regulations.

• MAXXUM T4E
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Magnum 235-340 (Series 4)
• Steiger series (350 to 600 HP)
• Puma series
• Farmall series

1. 1

   Visually inspect the DEF tank to confirm the actual fluid level. If the tank is empty or very low, the system is operating as designed.

2. 2

   Check the DEF tank, lines, and supply module for any physical leaks that could be draining the fluid prematurely.

3. 3

   Inspect the wiring harness and electrical connector at the DEF header unit (top of the DEF tank) for corrosion, moisture, or loose pins.

4. 4

   Use a diagnostic tool (like CNH EST or Jaltest) to monitor the live data from the DEF level sensor. If it reads empty while the tank is full, the sensor/header unit has failed or the float is stuck.

5. 5

   Check for DEF crystallization inside the tank, which can cause the level sensor float to stick in the 'low' position.

1. 1

   Refill the Tank

   If the tank is genuinely low, fill it with high-quality, uncontaminated Diesel Exhaust Fluid. Turn the key to the ON position and wait for the system to register the new level. The code should move from 'Active' to 'Inactive' and can be cleared.

2. 2

   Access the DEF Header

   If the tank is full but the code persists, disconnect the machine's battery. Locate the DEF header unit mounted on the top of the DEF tank.

3. 3

   Drain the Tank (If necessary)

   Depending on the machine model and tank location, you may need to drain the DEF fluid and drop the tank to access the header unit.

4. 4

   Remove the Sensor Assembly

   Disconnect the electrical connector and the DEF supply/return lines. Unbolt the mounting flange/seal and carefully pull the DEF header unit out of the tank.

5. 5

   Inspect and Clean

   Check the sensor for heavy crystallization. While sometimes it can be cleaned with warm distilled water, internal electrical failures of the level sensor require a complete header replacement.

6. 6

   Install New Part

   Insert the new DEF header unit into the tank, ensuring the mounting flange seal is seated correctly to prevent leaks.

7. 7

   Reassemble and Clear Codes

   Reconnect the fluid lines and electrical harness. Refill the tank with DEF, reconnect the battery, and use a diagnostic tool to clear the 19559 / F18F fault code. Verify the dashboard gauge now reads the correct fluid level.