• Engine Series:

  • Cummins B6.7 / ISB: Used in medium-duty trucks, school buses, and delivery vehicles.

  • Cummins L9 / ISL: Found in vocational trucks (dump trucks, refuse), transit buses, and emergency vehicles.

  • Cummins X15 / ISX15: Standard for heavy-duty Class 8 highway trucks.

• Model Years: Primarily covers engines from 2010 to 2024+ (EPA10, EPA13, EPA17, and later standards).

Common Vehicle Applications

• Freightliner: Business Class M2, Cascadia, 108SD/114SD.

• International: MV Series, HV Series, LT Series.

• Kenworth & Peterbilt: Medium-duty (T280/536) and heavy-duty (T680/579, T880/567).

• Transit & School Buses: Blue Bird, Thomas Built, Gillig, New Flyer.

• The Chemical Reactor: Inside the metal canister is a honeycomb structure coated with precious metals (like platinum or palladium). When hot exhaust gases pass through, a chemical reaction occurs that oxidizes carbon monoxide (CO) and unburnt fuel (hydrocarbons).

• Heat Generation: Its most vital role is to support the DPF Regeneration process. By oxidizing the fuel injected into the exhaust stream (via the HC doser), the DOC raises the exhaust temperature high enough to burn off the soot trapped in the downstream DPF.

• Passive Cleaning: During normal highway driving, the DOC helps convert Nitrogen Oxide (NO) to Nitrogen Dioxide (NO2), which helps the DPF clean itself "passively" without extra fuel.

• Maintenance: Unlike the DPF, the DOC does not trap soot, so it doesn't need "cleaning" in the traditional sense. However, it can become "poisoned" by low-quality fuel, engine oil leaks, or coolant leaks, which coat the catalyst and stop the chemical reaction.

• Incomplete Regeneration: The most common sign. If the DOC is "poisoned" (coated in oil or coolant), it cannot generate enough heat to burn soot in the DPF. You will see a "Regen Required" light that won't go away even after a parked regen.

• Face Plugging: If the engine has upstream issues (like a faulty fuel injector or EGR valve), a thick layer of soot can build up on the front face of the DOC, physically blocking exhaust flow.

• Low Temperature Fault Codes:

  • Code 1691: Aftertreatment 1 Diesel Oxidation Catalyst Efficiency - Below Normal.

  • Code 3167: Aftertreatment DPF Regeneration - Sustained Low Temperature.

• Blue or White Smoke: If the DOC fails to oxidize the fuel injected during regeneration, unburnt diesel will exit the tailpipe as thick white or blueish-white smoke.

• Engine Derate: If the module is severely plugged, backpressure will rise, and the ECM will cut engine power to prevent turbocharger damage.

• Raw Fuel Smell: A strong smell of diesel from the exhaust during a regeneration cycle suggests the catalyst is no longer active.