4394859NX | Genuine Cummins® Inlet Catalyst Module

Engine Platforms:

• Heavy-Duty: Cummins ISX15, X15, and ISX12.

• Medium-Duty: Cummins ISB6.7 and ISL9/L9.

Emissions Standards: Primarily used in systems meeting EPA10, EPA13, and EPA17 regulations.

Primary Vehicle Applications:

• Linehaul Trucks: Kenworth T680, Peterbilt 579, Freightliner Cascadia, International LT.

• Vocational & Specialized: Dump trucks, cement mixers, and fire trucks (E-One, Pierce).

• Buses: Transit buses and motorcoaches (New Flyer, Gillig, MCI).

Oxidation: It contains a ceramic honeycomb structure coated with precious metals that trigger a chemical reaction. It converts carbon monoxide (CO) and unburnt fuel (hydrocarbons) into CO2 and water.

Heat Generation: Its most vital role is to support the "regeneration" process. It oxidizes fuel injected into the exhaust stream to create the high temperatures (over 550°C) needed to burn off soot in the downstream DPF.

NO conversion: It converts Nitric Oxide (NO) into Nitrogen Dioxide (NO2), which acts as a catalyst to help the DPF clean itself naturally during normal driving (passive regeneration).

Housing: It provides the mounting points for the first set of temperature and pressure sensors that monitor the health of the entire emissions system.

Face Plugging: If you see a thick layer of black soot or white/grey ash on the inlet face of the catalyst, the module is "plugged." This restricts exhaust flow, leading to high backpressure, turbo lag, and increased fuel consumption.

Low Temperature Gain (Regen Failures): During a parked regeneration, the ECM monitors the temperature rise across the DOC. If the outlet temperature doesn't reach the required threshold (typically 1000°F / 540°C), the DOC is likely "poisoned" or its precious metal coating has degraded.

Oil or Coolant Soaking: If a turbo seal fails or an EGR cooler leaks, the DOC becomes "contaminated." You will notice blue or white smoke coming from the exhaust. A soaked DOC cannot generate heat and often cannot be cleaned—it must be replaced.

Thermal Damage (Melting): If too much raw fuel reaches the DOC (due to a leaking injector), it can cause an uncontrolled "torch" effect. This melts the internal ceramic honeycomb, which can sometimes be seen as a "sinkhole" or melted center when looking inside the unit.

Fault Codes:

• Code 1691: Aftertreatment 1 Diesel Oxidation Catalyst Efficiency - Data Valid but Below Normal Operating Range.

• Code 2639: Manualized DPF Regeneration - Data Valid but Below Normal.