What is an aftertreatment system? (...and why should I care?)


Why you really do want to know about your aftertreatment system 

Many drivers are in the dark about their aftertreatment system, let alone how to maintain them. And why not? It seems like a complicated system, there’s very little information about it, and there’s even less about how the maintenance affects your truck.  

Who’s going to bother with something they don’t even know is important?  

But consider this: maintaining your aftertreatment system is critical for the peak performance of your diesel-powered vehicle. It’s so important, in fact, that it affects your bottom line. 

How does aftertreatment system maintenance affect your bottom line? 

When any portion of your truck’s aftertreatment system becomes clogged it’s like your truck has indigestion. You may not notice at first, but after a while you’ll start to notice the noise.  

So, what then? Before long you have reduced efficiency and decreased engine performance, and ultimately your expensive emission components are damaged.  

Make sense? Ultimately this impacts your bottom line with unplanned downtime and costly repairs. 

So back to our original question … why would you want to know about your aftertreatment system? The health of your aftertreatment system affects almost every aspect of your truck.  

So, in this post we’ll explain how it works, so it will no longer be mysterious. Then you’ll be able to take care of potential problems before they cost you time and money. 

A little history of emissions control 

Emissions control is relatively new, so let’s consider a little history to put things in perspective.  

Air pollution was becoming undeniable in the 1950s, and by the early 1960s just sitting in rush hour traffic could make you nauseous. In time, large cities were plagued by smog and governments of developed countries were taking it seriously.  

So, the US government had legislation passed granting it the authority to address pollution. In 1974 it began to issue emissions policies. These policies were strict on final outcomes but allowed a phased approach to give manufacturers the time needed to develop effective solutions. 

Scrub the exhaust? 

In early 2000 (about 30 years after vehicle emissions control began), the heavy-duty truck industry began to feel its share of serious regulation. Of course, manufacturers knew these policies were coming, and they were prepared. Most of them proceeded with the Exhaust Aftertreatment System (EATS) to meet those regulations. 

Aftertreatment systems basically clean up the engine exhaust before it leaves the vehicle. We call this “scrubbing emissions from the exhaust gasses”. Every truck has exhaust, it just needs to be clean before it leaves the vehicle. 

Heavy-duty truck emissions controls were also phased in gradually. The first part of the EATS to be introduced was the EGR (Exhaust Gas Recirculation) system. In 2007 they added controls that included a DPF (Diesel Particulate Filter), and in 2010 added a process called SCR (Selective Catalytic Reduction).  

Sound complicated? It is (but we hope to uncomplicate it for you). Sound sophisticated? It’s that, too. And you probably know that anything that’s complicated and sophisticated needs to be well maintained or it’s going to cause you trouble. 

If you learn about it step-by-step to keep it simple, the system is also pretty interesting. We hope you’ll agree as you read on.  

What is the exhaust aftertreatment system and what does it do? 

The aftertreatment system cleans up particles and exhaust gases (nitrogen oxide), impacting performance as little as possible.  

Imagine an exhaust stream moving through the system. At each stage it’s getting a little cleaner, because at each stage it’s leaving some of its toxins behind. (If you’ve ever looked at a dirty DPF filter, you’ll know what we’re talking about.) 

And doesn’t it make sense that this system will need to be cleaned? That’s where the OTR diagnostic tool comes in. But we’ll get to that in a minute. First, let’s take a look at the components of the aftertreatment system. Hopefully, by the time we’re finished here, you’ll be thinking “oh, that’s not so complicated after all!” 

The 4 components of an aftertreatment system 

  1. Diesel Oxidation Catalyst (DOC) System 
    The engine's exhaust first goes through the DOC where the exhaust gases are oxidized to control carbon monoxide and hydrocarbon emissions. 

  2. Diesel Particulate Filter (DPF) System 
    The DPF is next. The DPF removes larger particulate matter from the exhaust stream. The DPF does a remarkable job at this as it typically removes over 99% of particulates. This explains why the DPF can get such a thick layer of soot. 

    Soot can be a real problem. As the layer of soot in the DPF thickens it produces back pressure and restricts forward movement. This back pressure will continue to build until you initiate a regeneration to remove the soot.   

  3. Diesel Exhaust Fluid (DEF) Injection 
    The next process is called DEF injection. DEF is a solution of urea and water that's injected into the exhaust stream to begin to transform the nitrous oxide (NOx). It decomposes in the hot exhaust to form ammonia, water, and carbon dioxide.

    This decomposed urea moves along with the exhaust to the next component, the Selective Catalytic Reduction (SCR) system.

  4. Selective Catalytic Reduction (SCR) System
    The SCR stage removes most of the remaining NOx. The decomposed urea and exhaust gases react with the active chemicals in the SCR to form carbon dioxide and water vapor. This is what exits the tailpipe.

    Cleaner exhaust fumes = a truck with peak potential 

    Aftertreatment systems are critical to the performance of diesel-powered vehicles. Their maintenance is often overlooked, typically from a lack of understanding. 

    As we said earlier, clogging any portion of the aftertreatment system will result in decreased engine performance, reduced efficiency, and damage to expensive emission components. The resulting unplanned downtime and costly repairs will wreak havoc with your truck and so … your bottom line. 

    Understanding what these systems do – and how they contribute to the overall performance of your vehicle – will help you maintain your aftertreatment system. Your dealership or technician can help you maintain the system, or you can easily (and more affordably) do it yourself with OTR diagnostics 

    OTR diagnostics is the affordable, easy-to-use tool that will help you keep your truck in peak performance. 

    Looking to learn more? Check out our other blog posts. 

      OTR diagnostics allows you to read and reset fault codes, view live data and run advanced diagnostic functions, including forced DPF regen with your mobile phone or tablet. Select which engine you have for your diagnostic package. 

      The OTR reset tool is specific to which model and engine you have. Select which engine for more specific details. 


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