Emissions critical: How to solve the aftertreatment diagnostics dilemma

“We have learned a lot about monitoring aftertreatment systems and optimizing preventive maintenance practices, and understand that using quality replacement parts, scheduling, and managing idle hours are critical,” explained Joe Puff, VP of truck technology and maintenance at NationaLease.

Still, Puff explained that training techs and drivers remains “the biggest aftertreatment challenge today.”

That’s because as these systems evolve, technicians need to stay up-to-date on all their service and component changes, as well as new issues that can spring up while staying proficient on previous versions. Even experienced troubleshooters can’t hit all of these moving targets.

It’s a reason why on diagnostic solutions provider Noregon’s 2025 “Unpacking the Commercial Vehicle Diagnostics Industry” report, 38% of the vetted respondents pointed to the aftertreatment system as the most challenging component to work on, just 2% behind the top answer, vehicle electronics, which stretch across the entire truck.

But for uptime to stay consistent, fleets must rise to meet the emissions challenges.

“Knowing how to properly diagnose and repair these systems is critical given how easily they can reduce an engine’s power output or shut it down entirely,” explained Jason Hedman, product manager at Noregon.

For example, at any time, a deterioration in the emission system’s performance may cause a truck to go into derate. This forces the driver to stop and manually force the emissions system to complete a regeneration cycle to burn off soot collected in the diesel particulate filter. Unless the derate was due to the engine not getting up to the correct temperature due to an on-road factor, such as excessive idling or an ill-timed traffic jam, there’s a problem only a proper diagnosis can sus out.

Finding out what the root cause is requires both properly trained techs and the right tools that can detect and repair issues on modern emissions systems. And even more changes are on the way to meet 2027 NOx standards. They also have to keep up with older trucks too, as Noregon’s report noted that 75% of heavy-duty trucks are already eight years old or more. Without the training, critical thinking skills, and tools, no fleet running diesel trucks will get very far. That’s why we caught up with several diagnostic experts to  explain why all three are vital.

No train, no gain

The most glaring issue is keeping shop techs up to speed on the evolving systems. Longer diagnostic time leads to a backlog of work in the shop.

Sandeep Kar, chief strategy officer at Noregon, attributes high shop dwell times for trucks to a generational skills gap and lack of proper troubleshooting devices. “Older technicians are having a hard time figuring out what these electronics are really spitting out in terms of information and insights, and younger technicians don’t have the right tools,” he told Fleet Maintenance.

But where should shops start? Diagnostic efficiency is likely a good place. Hedman explained that techs sometimes have a wasteful approach to troubleshooting and repair.

“A common mistake we see with aftertreatment system maintenance is technicians rushing to force a regen when they see an aftertreatment fault, rather than performing a proper diagnosis,” he said. “Unfortunately, an unnecessary regen can take a bit of time, burn fuel, and render the system too hot to work on for a while, so it leads to inefficiencies and lost profits in the shop.”

Not having enough training resources available seems to be another source of inefficient troubleshooting.

“One of the main challenges is the difficulty in accessing resources that make it easier to understand and resolve both mechanical and electronic issues, which are often very complex,” noted Jorge Verdejo, sales director at Cojali USA. “These resources go beyond tools—they include training or even online expert services that technicians can consult when needed.”

More online and in-person training with vendors is the long-term solution, but that takes time. For immediate training triage, the OEMs offer expert help through uptime call centers. On the vendor side, Noregon offers Technicians as a Service. This connects technicians stuck on a difficult job with remote experts who can walk them through that specific task while providing some teaching tips so they are more prepared for the next one.

“This reduces the need for less experienced mechanics to pull away a coworker from another job while ensuring the vehicle doesn’t face additional unplanned downtime,” Hedman said.

Emphasizing the root cause

But phoning a friend can’t be the default solution. For techs to advance as diagnosticians, they need to figure things out for themselves. To do that, they need to know how pumps, wires, and valves all interact with one another. But that doesn’t come easy.

“The biggest challenge is understanding how it all works,” offered Luke Powell, a technician at Fleet Pride in Lancaster, Pennsylvania.

Without figuring this aspect out, a technician will never see the full picture, and thus never achieve their full troubleshooting potential.

“Diagnosis is more about understanding the system; it’s not just one box or component, it’s multiple components from the turbo and EGR valve to the seventh injector and the DEF doser for the SCR system,” explained Michael DeMarinis, training and development manager at Boss Truck Shops.

DeMarinis noted all these systems are interconnected, requiring a tech to identify all the issues so they can properly perform a root-cause analysis.