By: Steve Hoke, Diesel Emissions Service

When NARSA/IDEA asked if I had any topics to write about, one came to mind quickly: How do DPF cleaning facilities troubleshoot overloaded or failed filters? And who do they share this information with?

Since DPF cleaning facilities make money by servicing DOC, DPF, and SCR units, how far do they go into telling the shop that dropped it off or the filter owner what the filter condition was? Or that a further look into the engine is necessary to keep from having more aftertreatment issues quickly?

Repair shops make money by doing repairs. If they remove a DPF for cleaning and its compromised or needs to be replaced, they need to dig deeper into the engine or run diagnostics to see why the engine has overloaded the DPF. No one person or shop should be installing a replacement filter without understanding and correcting the root cause of the failed unit they are replacing.

At Diesel Emissions Service, we have also seen several DPFs sent in for warranty that had been cleaned a few times within a short period. Once we dug further, we asked if a DOC efficiency test had been completed. The answer was “No,” and when we asked what repairs had been completed prior to the replacement DPF needing to be cleaned, we saw that an EGR cooler had been replaced. The shop did the replacement, and sent the truck on its way. Within a few weeks the truck needed the DPF cleaned, the cleaning facility cleaned and replaced the unit back into service. Then within weeks, the truck needed the DPF service again. This time, they told the truck owner the DPF must not be any good. They installed a new aftermarket unit. Another 30 days had passed, and the truck is showing high back pressure and the trucks owner takes the truck back to the shop and asks, “What the heck?!” The shop feels it must be from bad DPF and sends it in for warranty.

This is why repair shops, including DPF cleaning facilities, need to get involved in the troubleshooting process. The shop should have done a DOC efficiency test after the EGR cooler was found to be defective. The shop should have also done this same test after the filter plugged up several times and had to be cleaned.

In this scenario, if the DPF cleaning facility used a filter cleaning tracking program, they should have contacted the shop or customer and advised that engine diagnostics needed to be completed as it’s not normal to clean a DPF more than once a year or 75,000 miles under normal conditions.

The shop finally did a DOC efficiency test and replaced the poisoned DOC. Most people still don’t know that ethylene glycol from coolant and excessive lube oil can stop the regeneration features from a catalyst quickly.

Here’s the lesson: Anytime there is a DPF issue, we need to use diagnostic tools to help us see what’s happening with the aftertreatment system. Most failures to the aftertreatment system come from the upstream source, the engine. As a NARSA/IDEA member, you have access to several videos from different webinars that were done as part of the Lunch and Learn webinar series. These are available to view or have new employees watch to help in their training on

This technical article was originally published in the 2022 July/August issue of The Cooling Journal.