Case IH 19139 – Engine Control Unit (ECU) or Dosing Control Unit (DCU): DEF/AdBlue Quality sensor detects Water

The Selective Catalytic Reduction (SCR) system requires Diesel Exhaust Fluid (DEF) to be at a specific concentration (approximately 32.5% urea). This code triggers when the sensor detects that the DEF has been diluted with water, has severely degraded, or if the sensor itself has failed and is sending an out-of-range reading.

• Tier 4b
• Puma
• Maxxum
• Farmall
• Quadtrac
• Steiger
• SV340B
• TV380
• T5
• T6
• T7

1. 1

   Test the DEF fluid using a refractometer to ensure it reads exactly 32.5% urea. Do not immediately replace the sensor.

2. 2

   Visually inspect the DEF fluid for cloudiness, diesel fuel contamination, or crystallization.

3. 3

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

4. 4

   Evaluate the DEF quality sensor for internal failure (ammonia gas corrosion) if the fluid tests perfectly at 32.5% and the wiring is intact.

1. 1

   Drain contaminated fluid

   If the fluid is contaminated: Place a suitable drain pan under the DEF tank and completely drain the contaminated fluid.

2. 2

   Flush tank

   Flush the tank with distilled water or fresh DEF to remove residual contaminants.

3. 3

   Refill and test

   Refill with fresh, API-certified DEF, clear the codes with a diagnostic scan tool, and run an SCR dosing test.

4. 4

   Clean tank area

   If the sensor has failed (Fluid is verified good): Clean the area around the top of the DEF tank to prevent dirt from falling inside.

5. 5

   Disconnect electrical harness

   Disconnect the electrical harness connector from the DEF header/quality sensor assembly.

6. 6

   Disconnect fluid lines

   Disconnect the DEF suction and return lines from the header (be prepared to catch minor fluid spillage).

7. 7

   Remove retaining ring

   Unbolt or unscrew the retaining ring holding the DEF header assembly to the tank.

8. 8

   Remove old header

   Carefully pull the old DEF header unit out of the tank.

9. 9

   Clean mounting flange

   Clean the mounting flange on the tank to ensure a proper seal.

10. 10

    Install new header

    Insert the new DEF header/quality sensor assembly into the tank and secure it with the retaining ring.

11. 11

    Reconnect lines and harness

    Reconnect the DEF fluid lines and the electrical connector.

12. 12

    Clear codes and verify

    Use a diagnostic scan tool to clear fault code 19139 and run a system test to verify the repair.