Case IH 3995 – ISM-IDI ENGINE: Diesel Particulate Filter (DPF) OUT (Exhaust) Temperature is over 800 °C (1472 °F)

This indicates a critical over-temperature condition at the exit of the DPF. This typically happens during an active exhaust regeneration cycle if there is an excessive accumulation of soot, unburned fuel leaking into the exhaust system (which ignites and causes thermal runaway), or a failure of the exhaust gas temperature (EGT) sensor itself sending a falsely high voltage signal.

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1. 1

   Verify live sensor data for the DPF OUT temperature sensor using a diagnostic scan tool. If the temperature reads above 800 °C while the engine is cold, the sensor or wiring is shorted/faulty.

2. 2

   Inspect the wiring harness leading to the DPF OUT temperature sensor for chafing, melting, or short circuits to ground.

3. 3

   Check for related codes that might indicate the root cause, such as Delta P (Differential Pressure) sensor faults (3996, 3997), DOC intake temperature faults (3994), or fuel pressure/injector faults.

4. 4

   Inspect the DPF and DOC (Diesel Oxidation Catalyst) housings for external discoloration (bluing of the metal), which confirms an actual extreme heat event.

5. 5

   Verify that the Engine Controller (ECM) has the latest OEM software flash installed, as outdated software can mismanage regeneration temperatures.

1. 1

   Safety First

   Ensure the machine is turned off, the battery is disconnected, and the exhaust system has completely cooled down to avoid severe burns.

2. 2

   Locate the Sensor

   Locate the DPF OUT Exhaust Gas Temperature (EGT) sensor, which is threaded into the exhaust piping immediately downstream of the Diesel Particulate Filter canister.

3. 3

   Remove the Sensor

   Disconnect the electrical connector. Carefully loosen and remove the sensor using a line wrench or specialized sensor socket. (Penetrating oil may be required if the sensor is seized from heat cycling).

4. 4

   Inspect the DPF

   If the sensor was reading accurately and an actual thermal event occurred, inspect the DPF substrate with a borescope for melting, cracking, or face-plugging. If the substrate is melted, the entire DPF must be replaced.

5. 5

   Install the New Sensor

   Apply a high-temperature anti-seize compound to the threads of the new EGT sensor (if not pre-applied by the manufacturer). Thread it in by hand to prevent cross-threading, then torque to the OEM specification.

6. 6

   Reconnect and Clear

   Reconnect the wiring harness. Reconnect the battery, turn on the ignition, and use a diagnostic scan tool to clear the 3995 fault code.

7. 7

   Validation

   Start the engine and perform a forced stationary DPF regeneration via the scan tool. Monitor the DPF IN and DPF OUT temperatures to ensure they rise normally and stabilize safely below the 800 °C (1472 °F) threshold.