Case IH 3785 – Engine Control Unit (ECU) / Electronic Diesel Control (EDC): Diesel particulate filter (DPF) : Fault path for maximum number of locked regenerations.

The engine control system has locked out (disabled) the DPF regeneration process. This happens when the system has attempted to regenerate the DPF but failed too many times, or the operator has manually inhibited the regeneration process too many times. The ECU locks the regeneration path to prevent severe thermal damage, DPF melting, or a potential fire hazard caused by trying to burn off an excessive accumulation of soot and ash.

• Farmall
• Magnum
• Steiger
• Quantum
• Patriot

1. 1

   Read Soot/Ash Levels: Connect the CNH Electronic Service Tool (EST) or FPT EASy diagnostic tool to check the exact soot and ash load percentages in the DPF.

2. 2

   Check for Related Codes: Look for accompanying codes that indicate the severity of the blockage, such as: 3786, 3787, 3788, 3790.

3. 3

   Verify Differential Pressure: Monitor the live data from the DPF Differential Pressure Sensor (Delta-P sensor). If the pressure drop across the exhaust gases is excessively high, the filter is physically blocked.

4. 4

   Inspect for Upstream Issues: Check for exhaust leaks, intake leaks, or faulty fuel injectors. An underlying engine issue often causes the excessive soot that leads to a locked DPF.

1. 1

   Attempt Service Tool Recovery

   If the diagnostic tool shows the soot load is high but still within a recoverable threshold, use the CNH EST to command a 'DPF Recovery Regeneration' or 'Emergency Regeneration.' This overrides the lock if the ECU deems it safe.

2. 2

   Remove the DPF

   If the differential pressure is too high, the filter is completely clogged, or the recovery regeneration fails, the DPF must be physically removed from the exhaust stream.

3. 3

   Clean or Replace

   Send the DPF to a certified facility to be professionally baked and blown out (ash removal), or replace it entirely with a new OEM unit.

4. 4

   Inspect Sensors

   While the DPF is removed, inspect the DPF Differential Pressure Sensor and the exhaust temperature sensors. Clean the sensor tubes to ensure they are not clogged with soot. Replace the sensors if they are damaged or reading out of range.

5. 5

   Reset the ECU

   After reinstalling a cleaned or new DPF, you must use the CNH EST to perform a 'DPF Replacement' reset routine. This clears the locked state, resets the soot/ash counters to zero, and extinguishes the 3785 fault code.