Duramax Emission Systems & The Years Introduced

Modern Duramax trucks are engineered to meet increasingly strict emissions standards while maintaining performance, fuel efficiency, and reliability. From the early LB7s to the current L5P, GM has progressively refined the Duramax emissions systems using components like EGR valves, DPFs, SCR systems, and more.

Below is a breakdown of the emissions technology used in each generation.

• 2001 LB7

• • No EGR or catalytic converter.

• 2002–2004 LB7

• • ECM-controlled, vacuum-operated EGR with cooler. In 2002, California models received a catalytic converter.

• 2004.5–2005 LLY

• • Upgraded ECM with electric motor-actuated EGR valve and cooler. Catalytic converter included.

• 2006–2007 LLY–LBZ

• • Improved ECM with electric-actuated EGR valve, upgraded cooler, and catalytic converter.

• 2007.5–2010 LMM

• • Larger EGR cooler than previous models. DPF added; regeneration achieved via delayed injector timing and pulse injections to raise exhaust temperatures and burn soot.

• 2011–2016 LML

• • Enhanced EGR cooling, redesigned EGR valve, and an EGR cooler bypass valve. SCR and DEF systems introduced. Regeneration now handled by a ninth (indirect) fuel injector spraying diesel into the exhaust stream to reduce oil dilution.

• 2017–Present L5P

• • Reengineered EGR and emissions layout to meet stricter standards. Features a four-stage exhaust treatment system:

    • Close-coupled DOC (mounted directly behind the turbo)

    • SCR (Selective Catalytic Reduction)

    • Secondary DOC (Diesel Oxidation Catalyst)

    • DPF, working in tandem with EGR and DEF

Why Diesel Emissions Systems Matter

These systems reduce harmful byproducts from diesel combustion, including:

• Carbon Monoxide (CO) – from incomplete combustion

• Hydrocarbons (HC) – unburned fuel

• Nitrogen Oxides (NOx) – caused by high combustion temperatures

• Particulate Matter (PM) – soot from unburned fuel

*Advanced common-rail high-pressure fuel injection and precise timing have significantly lowered HC, CO, and NOx through more efficient combustion.

Emissions Components & Their Functions

EGR Valve

• Controls NOx by displacing oxygen and lowering combustion temperatures through the introduction of inert gases. NOx forms when temps exceed 2,500°F.

EGR Cooler

• Lowers the temperature of recirculated gases, making NOx reduction more effective.

EGR Bypass Valve

• Allows quicker warm-up of the combustion chamber and DOC during cold starts.

Diesel Oxidation Catalyst (DOC)

• Oxidizes HC and CO into CO₂ and H₂O. Converts NOx to NO₂ for further processing by the DPF and SCR.

Hydrocarbon Injector (Indirect Injector)

• ECM-controlled injector sprays diesel into the exhaust ahead of the DOC. This boosts exhaust temperatures for efficient aftertreatment.

Diesel Particulate Filter (DPF)

• Porous filter that traps PM/soot. Up to 90% efficient. Regeneration burns off collected soot once exhaust temps exceed 1,022°F.

Selective Catalytic Reduction (SCR)

• Reduces NOx to N₂, CO₂, and H₂O using DEF. DEF is a mix of urea and deionized water, delivering ammonia (NH₃) for the reduction reaction.