New Holland ENG 3979 – Engine ECU: Particulate Matter Catalyst (PMCat): Signal range check flow resistance of the particulate filter - Very High

The Engine ECU has detected an extremely high differential pressure across the Diesel Particulate Filter (DPF) / Particulate Matter Catalyst. This indicates severely restricted exhaust flow, typically because the DPF is completely clogged with soot or incombustible ash, or because the differential pressure sensor (or its hoses) has failed and is sending an erroneous high resistance signal.

• L218
• L220
• L221
• L223
• L225
• L228
• L230
• C227
• C232
• C238
• T4.75
• T4.85
• T4.95
• T4.105
• T4.115
• T4.F
• T4.N
• T4.V
• T5.95
• T5.105
• T5.115
• B95C
• B110C
• L213
• L215
• L216

1. 1

   Check for accompanying codes such as 3789 (Regeneration duration exceeds maximum allowed), 3796 (DPF pressure sensor hose line error), or 3798 (DPF pressure sensor error)

2. 2

   Visually inspect the rubber/metal hoses running from the exhaust pipe to the DPF Differential Pressure Sensor for melting, cracking, or blockages caused by hard soot buildup

3. 3

   Verify the voltage of the DPF differential pressure sensor to ensure it is not shorted to power or ground

4. 4

   Use a diagnostic tool to check the calculated soot and ash accumulation levels in the Engine ECU

1. 1

   Resolve Sensor/Hose Issues First

   If the diagnostic checks reveal melted or plugged differential pressure hoses, replace the hoses and clear the lines. If the sensor is faulty, replace the DPF Differential Pressure Sensor.

2. 2

   Attempt Forced Regeneration

   If the sensor and hoses are intact, the filter is genuinely restricted. Connect your diagnostic tool and initiate a forced parked regeneration.

3. 3

   Monitor the Regeneration

   If the regeneration fails to complete, or if the duration exceeds the maximum permitted time (triggering code 3789), the DPF is face-plugged or filled with incombustible ash.

4. 4

   Remove the DPF

   Unbolt the exhaust clamps and remove the Particulate Matter Catalyst / DPF assembly from the machine.

5. 5

   Clean or Replace

   A filter that is completely restricted with ash cannot be regenerated. It must be sent to a specialized facility for professional pneumatic/thermal ash cleaning, or replaced entirely with a new or remanufactured unit.

6. 6

   Reset the ECU

   After reinstalling a cleaned or new DPF, you must use a diagnostic tool to reset the DPF ash accumulator values in the Engine ECU and erase the existing DTCs.