UNITED STATES—Many car owners are unaware of their vehicle’s aftertreatment system and maintenance protocol. This is because aftertreatment systems seem complicated and there’s insufficient information about them.

In case you own a diesel-powered car, understanding how the system works and how to maintain it is necessary. Doing so will save you from unnecessary expenses accrued from poor maintenance. In this article, you’ll learn how an aftertreatment system works and how the greenhouse emissions produced from diesel combustion are converted into a less harmful state.

The Need For An Aftertreatment System

Your car’s aftertreatment system is designed to substantially reduce harmful emissions produced by the combustion of diesel fuel. It focuses on particular molecules emitted from diesel combustion and converts or processes them into non-hazardous byproducts. The molecules are present at different levels of engine operation and include Nitrogen Oxide (NOx), Hydrocarbons (HC), and Particulate Matter (PM).

Each state has its regulations on carbon emissions, but it’s generally recommended that all diesel engines must have an aftertreatment system. Most regulations focus on the percentage of emissions on highways and off-road trips, which exposes vehicles to high and low temperatures.

How It Works

An aftertreatment system comprises a diesel particulate filter (DPF) system and a selective catalytic reduction (SCR) system. The DPF system reduces the number of particles released by burnt diesel, while the SCR system reduces the nitrogen oxide (NOx) levels. When toxic gasses leave the turbo and enter the exhaust treatment system, the DPF, in combination with a diesel oxidation catalyst, picks up the accumulated carbon and oxidizes it to remove less harmful emissions through the exhaust. The emissions include:

  1. Low Engine Temperature Emissions

The engine is less likely to heat up if you often use your diesel-powered vehicle for off-road trips. Therefore, it emits particulate matter and hydrocarbons, which must be cleaned by the diesel particulate filter (DPF) system. And if your DPF system needs maintenance, you can click right here to see the different prices for parts and ship them at your convenience.

  • Particulate Matter (PM)

Particulate matter is the black particles seen leaving the exhaust pipe. It’s a product of partially burnt engine oil, hydrocarbons, and other components of diesel fuel. The PM is collected in the DPF by channeling the exhaust gasses via a ceramic filter. Continuous filtration leads to the accumulation of particulate matter in the filter system and requires cleaning.

During cleaning, the particulate matter is burnt and converted into ash through active and passive regeneration. In passive regeneration, the engine produces sufficient heat to burn off the PM. Conversely, in active regeneration, the engine doesn’t have enough heat to burn the PM in the DPF. Therefore, it’s forced into an artificial load that creates a high enough exhaust temperature to turn the PM into ash.

  • Hydrocarbons (HC)

Due to the low engine and in-cylinder combustion temperatures, hydrocarbons leaving the engine are usually unburnt. However, the hydrocarbons disappear as the engine warms up and the temperatures rise.

  1. High Engine Temperature Emissions

As opposed to off-road trips, highway trips allow you to accelerate without worrying about the state of the road. This acceleration increases engine and exhaust temperatures that completely burn the diesel to release (NOx), which consists of nitrogen dioxide (NO2) and nitrogen oxide (NO). The aftertreatment system contains urea (also known as diesel exhaust fluid DEF) and demineralized water at a combined concentration of 32%. The urea is sprinkled into the exhaust gas through a mixer before entering the selective catalytic reduction (SCR) system.

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Once in the SCR system, the urea vaporizes into ammonia and water. The ammonia attaches to the SCR catalyst and combines with the NOx as it passes over the catalyst. The resulting chemical reaction will release water and nitrogen gas into the environment.


If you want your diesel-powered vehicle to last longer, you should always strive to maintain its aftertreatment system. For example, the DPF section consistently collects particulate matter and is prone to clogging. You should therefore consider cleaning or replacing it at intervals recommended by your vehicle’s manufacturer.

The longer the diesel exhaust fluid (DEF) is used, the less pure it becomes, affecting the performance of the aftertreatment system. Modern trucks will always give a dashboard notification if the purity level has dropped. Failure to replace the DEF upon notice may lead to loss of the accelerator function, leading to more expenses.

Other parts needing consistent maintenance include:

  • The catalyst section
  • The nitrogen oxide inlet and outlet
  • Temperature sensors
  • The dosing module
  • The injector

Checking them all at once may be difficult, and sometimes, you may forget. It’s, therefore, necessary to have regular checks by a professional to avoid unnecessary inconveniences and play an active role in climate control.


Car aftertreatment systems are meant to reduce the number of greenhouse gasses released by diesel-powered engines. However, most owners fail to maintain their systems leading to engine failure. Moreover, some fail to meet government regulations on emissions and pay huge fines. You should seek to understand how the system functions and the various emissions produced during high and low engine temperatures. This knowledge will help you keep your vehicle in mint condition as you do your daily chores.