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Aftertreatment 101

Learn about common diesel aftertreatment terms from Redline Emissions Products®

The aftertreatment system is relatively new to the world of trucking and includes a lot of abbreviations/acronyms. Redline Emissions Products® is here to define the most common emissions industry terms and what they mean for you. (read all the way to the end and get a free download)

DPF – Diesel Particulate Filter

A DPF is an aftertreatment device designed to remove diesel soot (PM) from the exhaust stream of a diesel engine before it’s released into the atmosphere. DPFs have a PM (particulate matter) reduction rate of 85% – 100%; successfully oxidizing (burning) accumulated particles either passively (while the vehicle is driving down the road) or actively (through an outside heat, fuel, or electric source). DPFs need to be removed & cleaned regularly to avoid ash buildup & sintering.

Redline Emissions Products® offers a line of 100% new, direct-fit DPF replacements that are labeled with OEM cross numbers.

DEF – Diesel Exhaust Fluid

is a non-hazardous solution, which is 32.5% urea and 67.5% de-ionized water. DEF is sprayed into the exhaust stream of 2010 and newer diesel vehicles to allow the SCR to break down dangerous NOx emissions into harmless nitrogen and water. This is an integral part of the aftertreatment system, as the EPA has strict emissions standards for NOx. DEF presence is generally identified by a black plastic tank with a blue cap.

PM - Particulate Matter

PM – Particulate Matter

comprised of all solid and liquid particles suspended in air – many of which are hazardous. This complex mixture includes both organic and inorganic particles, such as dust, pollen, soot, smoke, and liquid droplets. One function of the aftertreatment system is to filter out the particulate matter before it can be released into the environment.

Aftertreatment 101 - DOC Diesel Oxidation Catalyst

DOC – Diesel Oxidation Catalyst

is an aftertreatment component that is designed to convert carbon monoxide (CO) and hydrocarbons into carbon dioxide (CO2) and water. It breaks down pollutants in the exhaust stream from a diesel engine, helping to reduce particulate matter (PM). Typically located before the DPF in the emissions system, it conditions the exhaust gases to allow the DPF to regenerate. Just like the DPF, if the DOC is not cleaned regularly, it can accumulate buildup, causing problems upstream & downstream.

Redline Emissions Products® offers 100% new, direct-fit DOCs for all makes, labeled with OEM crosses and ship with the required DPF gaskets.

aftertreatment 101 section - Oxidation


The process of converting exhaust gas pollutants into harmless gases.  In a DPF this process “burns” off the PM leaving the ash in the filter. 

Aftertreatment 101 - SCR Selective Catalytic Reduction

SCR – Selective Catalytic Reduction

an advanced active emissions control technology system that uses diesel exhaust fluid (DEF) sprayed through a special catalyst in the exhaust stream of a diesel engine. The SCR system reduces almost all of the NOx emissions. SCRs can be cleaned when the DEF dosing system malfunctions and the unit is filled with crystalized fluid.

Aftertreatment 101 - OEM Original Equipment Manufacturer

OEM – Original Equipment Manufacturer

a company that produces parts and equipment that may be marketed by another manufacturer, i.e., manufacturer of a specific truck brand. In terms like “OEM performance” and “OEM fit,” it means that a replacement fits & functions as well as the original.

You’ll find that all Redline Emissions Products® parts can boast OEM performance, fit, and function.

AFtertreatment 101 - Duty Cycle

DC – Duty Cycle

conditions in which the diesel vehicle operates on a daily basis. This is important to define as factors like load weight, miles driven, idling, & environment can all affect the wear rate on a vehicle.

Aftertreatment 101 - Back Pressure

BP – Back Pressure

the back pressure of a diesel engine; a measurement of exhaust gas pressure. Back pressure is carefully calibrated in a diesel engine, and a clogged DPF or DOC can cause problems such as increased fuel consumption and overheating of the engine.

Aftertreatment 101 - REMAN Remanufactured

REMAN – Remanufactured

Typically, is a component that has been disassembled and all wear parts replaced prior to reassembly. When used in reference to a DOC or DPF, a reman part is one that has been reconditioned (cleaned) and deemed okay for service. When considering a reman component, look for a warranty from the seller.

A remanufactured engine is usually more cost-effective than a new one and can be a great way to extend the life of a vehicle by hundreds of thousands of miles.

Caution, a reman part generally has a core charge.


make (a powdered material such as ash) coalesce into a solid or porous mass by heating it (and usually also compressing it) without liquefaction.  Sintering will reduce the usable mass of a DPF and is difficult or impossible to remove. 

You made it to the finish!

Here’s a free download of the infographic pdf for easy reference later. It includes all the common diesel aftertreatment terms, acronyms, and definitions covered and collected into a convenient and compact printable document.

Click the image to view and/or download

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Want to find out about becoming a Redline Emissions Products® dealer? Contact Wayne Cochrane, National Sales Manager for REP to find out more.  Call 888-295-4670

Need Tech Support or need help troubleshooting a DPF problem? No problem! Contact REP at 888-834-0050