How Does a Diesel DOC Work?

Diesel is a popular fuel due in part to its economy and the efficiency of diesel engines. However, diesel engines are (to use an overused expressed) well-oiled machines with critical, finely tuned components that improve not only fuel economy and raw power, but also provide pollution abatement.

Consider the diesel exhaust system, which helps remove toxins from emissions while recycling and regenerating particulate matter. Diesel exhaust systems typically contain a series of components, two of the most important of which are the diesel oxidation catalyst (DOC) and diesel particulate filter (DPF).

The diesel DOC is usually the first step in exhaust treatment, in which raw exhaust is passed to the DOC, a device containing a substrate that catalyzes the reaction of carbon monoxide (CO) and hydrocarbons (HC) with oxygen (that is, oxidation).

The diesel DOC converts CO to carbon dioxide (CO2) and hydrocarbons into water vapor by combining them with oxygen, thereby reducing the toxicity of these emissions.

Diesel exhaust gases also contain a portion of long-chain hydrocarbons known as soluble organic fraction or SOF. While the DOC is not particularly effective at oxidizing nitrogen oxides, it can be effective at converting NO to NO2.

Why a Functional DOC Is Important

There are two main reasons that a functioning DOC is important. One is that it helps keep the exhaust emissions compliant with EPA emissions standards; the other is that it can affect the soot loading limit of the DPF.

(The DPF, or diesel particulate filter, is another crucial component of the diesel exhaust system that helps remove particulate matter from the exhaust stream, further reducing pollution. It also recovers residual energy from unoxidized soot through two processes, known as active and passive regeneration, in which residual hydrocarbons are oxidized under higher temperatures, releasing additional energy.)

Together, the DPF and DOC are the two main components of the diesel exhaust aftertreatment system that limit pollution and improve engine performance and fuel economy.

Is a Diesel DOC the Same As a Catalytic Converter?

A diesel DOC is a type of catalytic converter that specifically helps to convert CO and HC emissions in diesel exhaust.

Should A Diesel DOC Be Periodically Inspected and Cleaned, Like a DPF?

Yes, like a diesel particulate filter, the diesel DOC should be periodically inspected and cleaned. The DOC is a “flow-through” device that can become what is called “face-plugged,” either limiting it or incapacitating it.

A good rule of thumb is to have the DOC inspected and cleaned any time you service your DPF, which will keep them on the same schedule.

Where Can You Get a New Diesel DOC?

Together, the DOC, DPF, and SCR help control diesel emissions by converting carbon monoxide and hydrocarbons into carbon dioxide and water under higher temperatures in oxygen-rich environments. They are all crucial components of the aftertreatment system.

If you need a new diesel DOC or DPF, visit Filter Service and Supply online at They carry a wide range of replacement parts and they also offer DPF cleaning services as well. If you have additional questions, get in touch with them at 760-455-0263.

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