Don’t ‘drive through the lights’ — and other aftertreatment system PM refreshers, tips

Daniel Mustafa, Assistant Manager of Technical Development for TravelCenters of America, says he still sees otherwise upstanding, wonderful people doing the kinds of things with their trucks that can turn a less-than-$1,000 major nuisance repair into a soul-crushing $11,000 one. When it comes to the aftertreatment systems on trucks with engines of 2007 and later emissions specs, price tags for poorly maintained units mount quickly given failure-related issues that happen down the line.

In the particular example he shared, a 2015 Kenworth came in after being driven through warning-light processes on the dash to the bitter end (the bottom icon in the image below). Repairing required not just baking/blowing the ash out of the particulate filter but replacing the diesel oxidation catalyst (DOC), just upstream of the particulate filter in the exhaust system, the DPF itself and a turbo, given excessive exhaust backpressure had damaged it.

Mustafa’s DPF warning-light breakdown
**1. (at top) The high exhaust temperature light indicates that passive regeneration is occurring. This occurs when the engine is under at least 50 percent of load, often when hauling on the heavier side at highway speeds. Regeneration, generally, is the process by which increased exhaust gas temperatures turn soot clogging portions of the DPF into less-clogging ash.
**2. The “you need a regen light,” as Mustafa calls it. When it comes on, the system needs to be regenerated, whether actively or passively. It starts solid, asking you “please,” Mustafa adds, then begins to blink to signal greater urgency, and your engine begins to derate, or reduce power output.
**3. The check engine light (yellow) starts with a 20 percent derate (reduction in horsepower output), then moves up to 40 percent, which if you hadn’t noticed the 20 percent, you will most certainly notice, Mustafa says. “Once you get to this point, you’re in trouble and you can’t do a regeneration yourself — you’re going to need a service center.”
**4. The stop engine light (red) — [Ominously] “engine damage is probable,” Mustafa quotes the Cummins manual, he says.Mustafa was speaking at the Expedite Expo Friday, July 14. His “don’t drive through the lights” message I imagine is well-heeded by the owners in this audience, and any owner with a working knowledge of their equipment, of course, but other maintenance considerations might be less apparent given the occasionally persnickety and relatively new nature of these systems. Knowing when exactly the filter is clogged enough to warrant a bake and/or blow-out (or in the case of Detroit’s post-2010 units still under warranty, employment of that company’s own fluid cleaning method so as not to void the warranty, he notes) is where a somewhat-new maintenance approach is advised.

Unlike with traditional approaches to oil changes and other service intervals — with hardfast intervals depending on the application and piece of equipment — it’s pretty hard to get a miles-to-clean maintenance interval for a DPF out of a service rep. Why?

“The difference could be hundreds of miles to hundreds of thousands of miles,” depending on the application, Mustafa notes, with vocational/urban/stop-and-go applications having much shorter intervals than long and heavy. “It’s very hard to nail somebody down to give you a maintenance interval.”

He recommends working “in conjunction with a service facility to gauge where you’re at” on the need to clean, a matter of “gauging the level of [exhaust flow] restriction in the DPF.” At 130,00 miles, he suggests, flow test the filter. Do it again at next service interval, then if OK at the one after that. “Work on it with some of your peers,” those with similar miles per gallon, driving style and application. All play a part, including amount of idle, which Mustafa recommends against to extend the life of the DPF and broader system. Intervals will be shorter, too, if your foot is fairly leaden. “If you’ve got a heavy foot, you make more soot” that needs to be burned off in regen, creating more ash that will eventually clog the filter.

For drivers engaged primarily in long-haul, with plenty of on-road time at greater than 50 percent of load on the engine, it might go as high as 200,000 to 225,000 miles before any need to shop-test the filter, Mustafa says. Get the cleaning done before it break, he adds, “and you’ll never have an issue.”