Case IH 3427 – Engine Control Unit (ECU): Diesel particulate filter (DPF): Signal range check flow resistance of the particulate filter - low.

The engine controller is detecting that the differential pressure across the Diesel Particulate Filter is abnormally low. The system expects a certain amount of exhaust flow resistance (backpressure) from the soot trapped in the DPF. When the resistance drops below the minimum threshold, the system suspects that the DPF has been physically removed, hollowed out, or that there is a failure in the differential pressure sensor circuit or its connecting hoses.

• Farmall
• skid steer
• Skid Steer Loaders (SSL)
• Compact Track Loaders (CTL)
• SR175
• Puma
• Steiger
• Magnum

1. 1

   Inspect the hoses running from the DPF exhaust piping to the differential pressure sensor for disconnections, cracks, melting, or leaks.

2. 2

   Inspect the wiring harness and connector for the DPF differential pressure sensor for shorts, corrosion, or open circuits.

3. 3

   Verify that the DPF has not been physically removed, bypassed, or hollowed out (DPF delete).

1. 1

   Inspect and Repair Hoses

   Locate the differential pressure sensor mounted near the exhaust system. Trace the two hoses back to the DPF. If the hoses are cracked, burnt, or blown off the fittings, replace them with high-temp OEM hoses and secure the clamps.

2. 2

   Test/Replace the Sensor

   If the hoses are intact and hold pressure, use a multimeter or diagnostic service tool to monitor the sensor's voltage/pressure output while the engine is running. If the sensor reads flat or out-of-range low despite actual exhaust flow, replace the DPF Differential Pressure Sensor.

3. 3

   Inspect DPF Substrate

   If the sensor and hoses are perfectly functional, remove the DPF housing and inspect the internal ceramic substrate. If the substrate is cracked, melted, or missing, the entire DPF assembly must be replaced.

4. 4

   Clear Codes

   After repairs, use a CNH diagnostic service tool (such as EST) to clear the fault codes and reset the DPF learned values/parameters. Run the machine under load to verify the differential pressure returns to normal operating ranges.