Case IH 19141 (DTC 4CCA) - ECU – Engine Control Unit (ECU): DEF/AdBlue quality sensor detects diesel fuel in DEF/AdBlue tank

The sensor has detected a critical substance (such as diesel fuel or another potentially destructive fluid) rather than the proper urea-based reagent (DEF/AdBlue). This condition will typically trigger a warning light, an engine power loss, or an SCR failure derate to protect the emissions system.

• MAXXUM T4E
• 240 Series Axial-Flow Combines (7240, 8240, 9240 Tier 4B)
• Maxxum
• Puma
• Magnum
• Optum
• Farmall

1. 1

   Visual and Olfactory Inspection: Open the DEF/AdBlue tank cap and check for the smell of diesel fuel or visual signs of cross-contamination (e.g., an oily sheen on the surface of the fluid).

2. 2

   Fluid Quality Test: Extract a sample of the DEF fluid and test its urea concentration using a DEF refractometer. Standard DEF should be at 32.5% urea.

3. 3

   Sensor Verification: If the fluid is perfectly clean and tests at the correct concentration, the DEF quality sensor itself may have failed, drifted, or suffered internal circuit board corrosion (a known issue where ammonia gas corrodes the sensor's electronics).

4. 4

   Wiring Check: Inspect the wiring harness and connector at the DEF header/quality sensor for signs of damage, corrosion, or a short circuit.

1. 1

   Drain the Tank

   If diesel fuel or contamination is confirmed, completely drain the DEF/AdBlue tank. Do not run the engine, as pumping contaminated fluid can destroy the DEF dosing pump and SCR catalyst.

2. 2

   Clean the System

   Flush the DEF tank thoroughly with distilled water or fresh DEF to remove all traces of diesel fuel or contaminants.

3. 3

   Replace the Sensor/Header (If Damaged)

   Diesel fuel can permanently damage the ultrasonic or optical components of the DEF quality sensor. If the sensor is damaged, or if the code was caused by a false reading from a failed sensor, remove the DEF header assembly from the top of the tank and install a new DEF quality sensor or complete header unit.

4. 4

   Refill and Prime

   Refill the tank with fresh, high-quality DEF/AdBlue.

5. 5

   Clear Codes

   Connect the CNH diagnostic tool (EST) to clear the fault codes and reset the SCR system. Run the machine to verify that the ECU reads the correct DEF quality and the derate is lifted.