Case IH 19076 – Engine Control Unit (ECU / EDC - Electronic Diesel Control): NH3 Slip behind SCR detected

Unreacted ammonia (NH3) from the Diesel Exhaust Fluid (DEF/AdBlue) is passing completely through the Selective Catalytic Reduction (SCR) catalyst and the Clean Up Catalyst (CUC). Because downstream NOx sensors are cross-sensitive to ammonia, the system uses the NOx sensor to detect this "slip".

• Tier 4b
• Case IH agricultural equipment
• Case Construction equipment
• 580N series backhoes
• FPT Tier 4 Final and Stage V engines
• 3.4L F5BFL413C
• 4.5L NEF
• Cursor engines
• Farmall 110A-140A
• Magnum 180

1. 1

   Test the DEF/AdBlue concentration using a refractometer (incorrect fluid cause). Urea concentration significantly above 32.5% or contaminated fluid will cause an NH3 slip.

2. 2

   Perform a NOx Sensor Overrun Test by driving the machine and measuring the downstream NOx sensor signal during deceleration (faulty sensor cause). The sensor must indicate < 30.00 ppm.

3. 3

   Run the Urea Dosing Leak Check (UDLC) and Urea Dosing Valve Check (UDVC) via diagnostic software (leaking doser cause) to verify the DEF injector is not leaking fluid into the exhaust when closed or over-dosing when open.

1. 1

   Address Fluid Issues

   If the DEF fluid failed the refractometer test, drain the DEF tank, flush the system, and refill with fresh, OEM-specification DEF (32.5% urea).

2. 2

   Replace the NOx Sensor

   If the downstream NOx sensor failed the overrun test (reading > 30.00 ppm during deceleration), remove the old sensor from the exhaust pipe downstream of the SCR and install a new one.

3. 3

   Replace the DEF Dosing Valve

   If the UDLC or UDVC tests reveal that the DEF dosing valve is leaking or stuck open, depressurize the DEF lines, unbolt the dosing valve from the exhaust mixing pipe, and install a replacement valve.

4. 4

   Replace the SCR / CUC Catalyst

   If the dosing system is functioning perfectly, the fluid is correct, and the NOx sensor is accurate, the Clean Up Catalyst (CUC) located at the end of the SCR has failed to convert the NH3 slip to nitrogen and water vapor. The SCR/CUC assembly must be replaced.

5. 5

   Reset Counters

   After repairs, use the diagnostic tool to clear the fault codes and perform a "Counters Reset" for the SCR system.