Onsite Truck & Equipment Repair Blog

Ignoring Your Diesel Truck's Exhaust Aftertreatment Systems Can Be Costly


As a fleet owner, we know how tough it can be scheduling service appointments, managing operators, hiring drivers, handling payroll, and networking with other businesses. And, even with all of your administrative duties, you also have to think about how to get the most out of the trucks in your fleet without missing a beat. From tires to engines, keeping your fleet’s various systems in check can help you increase your return on investment.

One system that you never want to ignore is your exhaust aftertreatment system, as a small slip-up like missing or forgetting about a DPF cleaning appointment can lead to a whole world of consequences for your business—fines and penalties from failed emission control tests, poor engine performance due to irregular combustion temperatures, and health concerns for your operators, to name a few. 

If you push your diesel truck’s exhaust aftertreatment system needs to the side, you’ll be shooting yourself in the foot. In this blog post, we’ll discuss why. 

Modern Diesel Engine Aftertreatment Systems

Following the creation of an emissions control agenda set by the Emissions Protection Agency (EPA) in 1985, emissions regulations have become more and more strict and restrictive over the past three decades. During this period, manufacturers had to adapt quickly; they had to change the status quo, faster than ever before. This led to the creation and evolution of diesel engine aftertreatment systems, which was a success—nitrous oxide (NOx) and particulate matter (PM) emissions fell by 95% and 90%, respectively.

But in order to reach this new, ultra-low NOx standard, research & development teams had to think outside the box. Their solution? A sophisticated and complex system spanning the length of your truck, with multiple subsystems working in tandem to reduce both NOx and PM emissions. 

How do engine aftertreatment systems work?

A typical aftertreatment system includes a diesel oxidation catalyst (DOC), diesel particulate filter (DPF), diesel exhaust fluid (DEF) injector, and selective catalytic reduction (SCR) chamber, all positioned at various “checkpoints” in your truck’s exhaust process to filter and eliminate NOx and PM. 

At the first checkpoint, exhaust fumes will pass through the DOC, which is a subsystem dedicated to reducing PM and oxidizing carbon monoxide and hydrocarbons. In this oxidization process, the DOC produces the necessary NO2 for the DPF to burn trapped NOx effectively. It also serves as a source of heat for DPF regeneration cycles during cold weather.

Second on the list is the DPF, a leader in NOx filtration. Accounting for more than 80% of NOx emission control, DPFs are positioned near the front of the after-treatment system and behind the DOC to capture and burn soot particles over frequent, automatic intervals.

Once the exhaust gases filter through the DPF, they’ll pass through a section of the pipe called a “mixing chamber,” where a DPF injector lies. This component is in charge of introducing a reduction agent (the DEF), a chemical solution that reduces NOx in the stream and converts it into harmless nitrogen and water.

The SCR is the last checkpoint at the tail-end of the aftertreatment system. This is where DEF and exhaust fumes mingle until the resulting exhaust gas isn’t really an “exhaust” gas anymore. At this point, the stream coming from the combustion chamber will be sufficiently broken down, filtered, and mixed with chemicals until the result is nothing more than nitrogen and water vapor.

The Importance of Proper Maintenance

A blown head gasket will cause overheating and inefficient performance. A clogged fuel filter will cause a decrease in engine performance. But a failing aftertreatment system will make you want to give up for the week—it’ll bring a whole world of trouble, including decreased miles per gallon, increased maintenance costs, reduced uptime, non-compliance with federal regulations… the list goes on and on. Simply put, if you neglect aftertreatment maintenance and repairs, you’ll be breaking the bank.

To prevent these issues from ever occurring, here are a couple of steps you can take:

  1. Fix air leaks

One of the most significant causes of aftertreatment-related downtime is a clogged DPF caused by a pesky air leak. If one of your operators is experiencing increased fuel consumption, it’s important you get your truck checked for air leaks prior to doing anything else. A plugged DPF is unable to produce sufficient temperature to burn PM, which could render the DPF inoperable, triggering a replacement. 

  1. Address Engine Issues

The aftertreatment system is designed to work with a healthy engine. As such, problems with your truck’s fuel system, engine oil, and coolant system are all culprits for contaminated aftertreatment components, which can lead to premature DPF cleaning, DOC or SCR damage, and much more. 

When getting your engine checked, make sure you’re using high-quality oils, lubricants, components, and parts (especially head gaskets, valves, and clamps) to ensure sealed intake and exhaust systems and no oil oxidization.

  1. Follow Recommended Maintenance Schedules

Like with any other mechanical or electrical system in your truck, we suggest you stick to a maintenance regime with a trusted repair shop. Not only will this help keep your fleet in tip-top shape, but it’ll also help you set DPF cleaning intervals, prevent air leaks, change low-quality oil and fluids for their fresh, high-quality counterparts, and inspect for damage.

Final Words

Ignoring aftertreatment systems can be very costly for heavy-duty fleet owners and managers. By fixing air leaks, ensuring engine health, and following recommended maintenance intervals, you can help prevent aftertreatment issues—it’s just a matter of paying attention to your fleet’s needs.

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