Common Problems: DPF Turmoil

What's the deal with regen?

May 2018 Feature Colin Peterson

If you haven’t heard the term “regen” yet, you’ve probably never owned a newer diesel, nor known someone well who owns one. Many problems on trucks manufactured in 2007 or later have something to do with the components of the dreaded after-treatment system, including the diesel particulate filter (DPF) and its process of regeneration. When the US Environmental Protection Agency (EPA) implemented a new set of regulations in 2007, we said a big “goodbye” to simple exhaust systems. With the new after-treatment systems installed on trucks since then, soot gets turned into ash through the heat generated by the chemical reaction of a diesel oxidation catalyst (DOC). It’s a very disadvantageous system, as it drastically lowers fuel mileage while the ash builds up on the DPF. Through the process of regeneration, the ash gets burned off; this process must occur on a regular basis to prevent serious engine damage.

What Is Regeneration?

Regeneration isn’t a very time-consuming process, but it must be done if you want to safely keep your precious truck. When the light with the exhaust symbol goes on, it’s time to regenerate. DO NOT IGNORE IT OR PUT IT OFF! Passively, regeneration can be done through normal exhaust system heat by driving at highway speeds for a half hour or so; if you’re making a long road trip, this is very convenient, because the truck will regenerate automatically after the light goes on. When driving in the city, however, the exhaust likely won’t get hot enough for an uninterrupted regeneration. That’s when it’s time to take the truck to the shop to perform a stationary regeneration. Because of the extreme complexity of the DPF system, the regeneration process is often extremely temperamental. If the process doesn’t run to completion or doesn’t run properly, it can cause other problems that could lead to engine damage because it puts backpressure on the engine and cripples performance.

To help explain what customers should look out for on their trucks, we spoke with Master Technician Brock Carter of Broadway Ford, and service manager John Giannini, Jr. of Smith Chevrolet, the dealerships near our offices in Idaho Falls, Idaho.

Common Problem #1: Excessive And/Or Ineffective Regeneration

Yes, excessive regeneration is a problem that is all too common, especially for the pre-2010 engines. The engines can easily shove too much soot into the DPF for the regeneration process to handle. That’s when the DPF gets clogged. The excessive soot itself can be caused by normal stop-and-go driving in densely populated areas, but the problem is more noticeable when the likely causes are over-fueling injectors, EGR problems, or turbo failures. Engine oil or EGR coolant can also get thrown into the exhaust from such upstream failures and add to clogging.

“Intake air leaks can even contribute,” adds Giannini. “The engine is not getting enough air for the amount of fuel being injected. That situation produces more soot and will work the regeneration process harder as well.”

Eventually, the DPF could become too clogged for any regeneration process to even work, which eventually results in total failure of the after-treatment system. In that case, the entire expensive system will need to be replaced. You’ll know if the system is about to fail if the exhaust makes an unusually loud whistling noise. One of the best ways to address this issue and prevent system failure is to use additives to help the fuel burn cleaner. An example of such would be AMSOIL’s Diesel Concentrate.

“Also, be sure you’re using the right fuel for the right time of year,” suggests Giannini. “Don’t use #2 Diesel during the winter.”

You can also reduce regeneration by running your truck on the highway more often. “People are not letting their trucks get up to speed to let the DPFs burn off. That’s what makes them clog,” the Chevy service manager says with determination. “To prevent that, I recommend the owner to hop on the highway and drive about 20 to 30 minutes at least once during the day.”

These problems can still occur on engines manufactured in 2010 or later, but they don’t happen as often, because these engines use diesel exhaust fluid (DEF) with their selective catalytic reduction (SCR) systems to help expedite the DPF cleaning process.

Common Problem #2: Fuel Contamination In Oil

Contamination is one of the most common problems triggered by regeneration itself, especially in 2007-2010 diesels. In many of these engines, regeneration works as the injectors spray fuel into the exhaust (during the exhaust stroke) that eventually gets burned as it reaches the DPF to counter the soot accumulation. Unfortunately, some of that fuel slips past the piston rings and begins to mix with the oil, which creates dangerous operating conditions that can cause severe engine damage if not quickly addressed.

“The engine will throw a code (and put a light on the dash) when there’s variance in the crank position sensor, which tells you that the oil level is rising,” says Ford Tech Carter. “You’ll be better able to tell if you check the oil frequently, as it’s contaminated with fuel if it appears light and high.”

For this reason, it is very important to check your oil on a regular basis. Complete engine failure is one of the last things you’ll want to experience. In helping prevent this, it is crucial to use properly formulated, high-quality engine oil, such as AMSOIL Synthetic OE 15W-40. On the 6.4L Power Stroke, do not follow Ford’s recommended 10,000-mile intervals; it’s very important to keep oil changes closer to every 5,000 miles to prevent damage to the DPF system. It’s good to do similar practices on the LMM Duramax.

“If you’re doing a lot of short drives, change the oil more often,” advises Giannini. “Keep the interval around 3,000 miles. Also, GM recommends you change the filter every 12,000 to 15,000 miles.”

It even helps to use a bypass oil filter, which features a valve that opens and closes accordingly so the engine does not starve for oil if the pressure differential across the filter becomes too high. GM has addressed this issue by installing an injector before the DPF on the exhaust system for the LML Duramax, so the engine won’t need to go out of its way to activate the regeneration cycle.


With the state of emissions regulations that we’re currently in, diesel vehicles are only becoming more complex and touchy to maintain. Manufacturers have had to add on to existing emissions control systems that barely worked well enough as it was to make trucks cleaner. EGR systems have increased soot levels inside the 6.0L Power Stroke, for example. Adding after-treatment systems to the EGR on the 6.4L Power Strokes has only made those matters worse, since when the EGR system malfunctions, it clogs the DPF more quickly.

“If the EGR isn’t functioning properly, it will easily plug up the DPF,” says Carter. “You’re bound to have serious issues if it happens. This is a great example of why you must not ignore that light on the dash.”

Engines are up to 30 percent less fuel efficient as a result of using DPFs. Not only does the after-treatment system reduce fuel economy by putting backpressure on the engine, but it also reduces efficiency by requiring injectors to spray extra fuel to actuate regeneration.

Overall, while there is no true way to fix these problems, you can still practice better driving and maintenance habits to deflect symptoms of regeneration problems, such as changing the oil every 5,000 miles or less, using high-quality oil, using additives in the fuel, driving at highway speeds at least once per day of driving, and only applying whatever throttle is necessary under all driving circumstances. As all repairs go, remember to always address your dash warnings if you want to make maintenance easier for yourself!




Broadway Ford






Ryder Blog

Smith Chevrolet


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