Case IH 3984 – Engine Control Unit (ECU) / Dosing Control Unit (DCU): SCR dosing, time to closed loop too long

The system takes too long to enter closed-loop dosing mode. This typically occurs because the exhaust temperature is not reaching the required threshold fast enough, the NOx sensors are failing to reach their operating temperature (dew point), or there is a mechanical issue with the DEF dosing module (pump/valve) preventing it from building pressure and injecting fluid.

• Maxxum
• Puma
• Magnum
• Steiger
• Farmlift
• T6
• T7
• W110 D
• W130 D
• W170 D

1. 1

   Check DEF/AdBlue quality and level to ensure the tank is full and the fluid concentration is correct at approximately 32.5 percent urea.

2. 2

   Check for accompanying fault codes related to NOx sensors (e.g., 3521, 3528, 3529, 3530), exhaust temperature sensors, or DEF pressure, as these will prevent the system from entering closed-loop mode.

3. 3

   Monitor exhaust temperatures upstream and downstream of the SCR catalyst to verify they are reaching the required operating temperatures for dosing.

4. 4

   Verify NOx sensor operation to check if the upstream and downstream sensors are reaching their dew point and providing plausible concentration readings.

5. 5

   Inspect the DEF dosing system by checking the pump for proper pressure build-up and the dosing valve for blockages or crystallization.

6. 6

   Check for exhaust leaks in the piping before the SCR catalyst that could cause a loss of heat or pressure.

1. 1

   Connect Diagnostic Tool

   Connect the CNH Electronic Service Tool (EST) to the machine's diagnostic port to read all active and logged fault codes.

2. 2

   Perform System Tests

   Use the EST to perform a DEF dosing system leak test and a pressure test to verify the dosing valve and supply module (pump) are functioning correctly.

3. 3

   Run a Forced SCR System Test

   Initiate a forced SCR system test or regeneration to monitor exhaust temperatures and NOx sensor readings in real-time.

4. 4

   Replace Faulty Components

   If a NOx sensor is slow to respond, fails to reach its dew point, or shows an open/short circuit, replace the affected NOx sensor. If the DEF dosing valve is blocked and cannot be cleaned of crystallized urea, replace the dosing valve.

5. 5

   Clear Codes and Validate

   Clear the fault codes. To validate the repair, the machine must be operated under load (e.g., minimum 50% load for approximately 20 minutes) to ensure the exhaust reaches the necessary temperature and the system successfully enters closed-loop dosing.