When working properly, aftertreatment systems clean exhaust gases to ensure diesel engines meet emission regulations. But aftertreatment systems remain the source of much confusion and frustration for fleets and drivers alike.

Like most everything else on a truck, these systems require regular inspection and maintenance for optimum performance.

To get the nitty-gritty on aftertreatment, the HDT Talks Trucking podcast brought on two experts: Steve Hoke, president of Redding, California-based Diesel Emissions Service, and Steve "Junior" Stratton, warranty and training manager at DES.

With nearly three decades of combined experience cleaning and servicing aftertreatment systems, Hoke and Stratton offered their thoughts on what can go wrong with these systems and how to maintain them for the best results.

Why is Diesel Aftertreatment Such a Headache?

Why do aftertreatment systems still seem to be causing grief for fleet managers?

“We believe that it's a lack of training and support from the OEMs, mainly because they want the vehicle brought back to the dealer for work,” Hoke told HDT Talks Trucking host Jim Park.

“With the 2007 and newer vehicles, mechanics had to become technicians and really learn and understand the new aftertreatment technology to be able to diagnose the systems,” he continued. “As far as the DPF or aftertreatment, in 2007, fleets were kind of thrown into a tailspin with downtime and costs attributed to the aftertreatment system.”

Hoke also said there was an unrealistic expectation of the expected performance of these systems.

“In 2007, almost every truck/engine manufacturer basically said, ‘Look, the aftertreatment systems are going to last 500,000 to 600,000 miles. Don't worry about them.’ But we found out over the years that things were a lot more complicated than that.”

He added that duty cycles for vocational trucks make it more difficult on the aftertreatment system to operate properly, compared to the steady-state operation of engines in long-haul, over-the-road trucks.

Even in on-highway trucks, however, things can go bad seemingly very quickly with an aftertreatment system, including causing roadside breakdowns.

“It's a culmination of things,” Stratton said. “It's a combination of duty cycle, lack of maintenance, and neglect. And then there are the rare occasions where there's an actual aftertreatment system failure.”

Dig Into the Causes of Aftertreatment System Problems

Hoke said that if he had a fleet of trucks that was having the types of downtime issues many fleets have reported, “I would be digging into the diagnostic side to find out why. Yep, I have opacity issues on the engine. Do I see temperatures that are not conducive to create a passive regen? Do I have a DPF that is plugged? No good. Do I have an SCR [selective catalytic reduction] system issue? Because theoretically, unless you are stopping, in the normal use of that vehicle it should be able to support either passive or active regens without your knowledge.”

In discussing some of the big picture around aftertreatment maintenance, Stratton invoked the tried and true “pay me now or pay me later” scenario.

“Fleets don't want to spend $350 to have a DPF cleaned, but do they want to spend $1,500 on a tow bill and three days in the shop? If they schedule the DPF cleaning on their own time with their own machines, they’re going to potentially save exponentially on the other end.”