5 Common Aftertreatment System Issues and How to Fix Them

Aftertreatment systems play a critical role in reducing emissions and ensuring compliance with environmental regulations. These systems are designed to filter harmful pollutants from the exhaust of diesel trucks, making them a vital part of modern heavy-duty vehicles. However, aftertreatment systems aren't immune to issues, and when they fail, it can lead to serious downtime and expensive repairs.

In this article, we’ll break down five common aftertreatment system issues and provide tips on how to fix them. Whether you’re managing a fleet in Strafford, MO, or working on your truck’s emissions system, understanding these problems and their solutions can save you both time and money.

1. Diesel Particulate Filter (DPF) Clogging

DPF clogging is one of the most common issues faced by heavy-duty diesel truck operators. The DPF is designed to trap soot and other particulate matter from the exhaust. Over time, this filter can become clogged if the engine isn’t running hot enough to trigger regeneration, a process where the trapped soot is burned off.

Symptoms:

• Reduced engine performance
• Increased fuel consumption
• Warning lights indicating DPF blockage

Fix:

The most common solution is to perform a regeneration cycle, either passively or actively, to burn off the accumulated soot. Passive regeneration happens when the truck is running at highway speeds and the exhaust system is naturally hot enough to clear the filter. If passive regeneration doesn’t occur, an active regeneration can be initiated manually. In some cases, forced regeneration might be needed, which requires specialized equipment to perform.

Learn more about how aftertreatment systems work by visiting this Cummins resource.

2. Faulty Diesel Oxidation Catalyst (DOC)

The Diesel Oxidation Catalyst (DOC) is another essential component of the aftertreatment system. It converts harmful carbon monoxide and hydrocarbons into less harmful substances like carbon dioxide and water vapor. When the DOC fails, it can disrupt the entire emissions system, causing increased emissions and reducing the efficiency of the DPF and SCR systems.

Symptoms:

• Increased black smoke from the exhaust
• Failed emissions tests
• Engine warning lights related to emissions

Fix:

If your DOC is failing, a replacement is often the best solution. It’s important to diagnose the issue early, as a failed DOC can cause additional strain on the DPF, leading to further issues down the line. Regular inspections and proper maintenance can prevent the need for frequent DOC replacements.

For more insights on emissions technology, check out this emissions guide from Perkins.

3. Selective Catalytic Reduction (SCR) Malfunctions

The SCR system plays a crucial role in reducing Nitrogen Oxide (NOx) emissions by injecting Diesel Exhaust Fluid (DEF) into the exhaust stream. This triggers a chemical reaction that converts harmful NOx into harmless nitrogen and water vapor. When the SCR system malfunctions, it can lead to increased NOx emissions and potentially large fines for non-compliance with emissions standards.

Symptoms:

• NOx sensor faults
• DEF warning lights
• Failed emissions tests

Fix:

The most common issue with the SCR system is the quality of the DEF. Make sure you're using the correct DEF mixture and storing it properly. If the DEF injector becomes clogged, cleaning or replacing the injector may be necessary. In some cases, sensor replacement may be required, as faulty sensors can lead to improper DEF dosing.

For specialized repairs related to the SCR system, visit our aftertreatment repair page here.

4. Exhaust Gas Recirculation (EGR) Valve Failure

The EGR valve is responsible for recirculating a portion of the exhaust gases back into the engine to lower the combustion temperature, thereby reducing NOx emissions. Over time, the EGR valve can become clogged with carbon deposits, leading to reduced engine performance and increased emissions.

Symptoms:

• Rough idling or stalling
• Poor fuel efficiency
• Excessive black smoke from the exhaust

Fix:

In many cases, the EGR valve can be cleaned to remove the carbon buildup. If the valve is severely damaged, a replacement may be necessary. Regularly cleaning the EGR valve and the related passages as part of your maintenance schedule can prevent buildup and extend the life of the component.

5. DEF Crystallization and Clogging

DEF crystallization occurs when the fluid evaporates and leaves behind solid urea crystals. These crystals can clog the DEF injector or other parts of the aftertreatment system, leading to inefficient operation and potential system failure.

Symptoms:

• Crystallized DEF around the injection points
• Decreased DEF system efficiency
• DEF-related warning lights

Fix:

To fix DEF crystallization, the injector and related components should be cleaned thoroughly. Regularly flushing the DEF lines and using high-quality DEF can reduce the risk of crystallization. It’s also important to store DEF properly, as exposure to heat and air can cause the fluid to degrade and crystallize more quickly.

For expert aftertreatment system repairs and maintenance, visit our shop in Strafford, MO or check out our aftertreatment repair services here.

Conclusion

Dealing with aftertreatment system issues can be a major headache, but with regular maintenance and early diagnosis, many of these problems can be avoided or easily fixed. Keeping up with DPF cleaning, checking your DEF quality, and ensuring that your EGR and SCR systems are functioning properly will not only save you time and money but will also keep your truck compliant with emissions standards. If you're facing any of these common aftertreatment issues, don't hesitate to seek professional help from a trusted repair shop.

For more in-depth information on aftertreatment systems, check out our company articles or contact us for repairs in Strafford, MO.