Emissions systems keep modern trucks legal, and they cause a big share of the calls we get.
The diesel particulate filter (DPF) traps soot and has to burn it off through regeneration. The SCR system needs clean diesel exhaust fluid (DEF) and working sensors to cut NOx. When any link in that chain fails, the engine computer steps in with lamps and, eventually, a derate.
Plenty of Knoxville trucks run a duty cycle that makes this worse. Local delivery, stop-and-go on I-640 and Kingston Pike, jobsite idling, and yard work rarely give the exhaust enough steady heat to clean the filter. Cold weather adds its own trouble: DEF freezes at about 12°F, and heaters, lines, and sensors that are marginal in October tend to fail in January.
We come to the truck, read the aftertreatment codes and live data, and figure out whether the fix is a regen, a sensor, a DEF system repair, or something that needs a shop.
What’s included with our DPF, DEF & Regen Service
- Parked (stationary) and forced regens with diagnostic software, when conditions allow
- Finding out why a truck won’t regen on its own — bad sensors, exhaust leaks, or regens that keep getting cut short
- DPF differential pressure sensor and sensor line replacement
- Exhaust gas temperature (EGT) sensor replacement
- NOx sensor diagnosis and replacement, inlet and outlet
- DEF pump, DEF heater, and dosing valve troubleshooting
- Clearing crystallized DEF from dosing valves and lines
- DEF quality problems — draining bad fluid and refilling the tank
- DEF level and quality sensor faults
- Aftertreatment fuel doser checks on engines that use one
- Exhaust leak repairs at clamps and gaskets that throw off sensor readings
- Clearing derates once the underlying problem is fixed
What needs a shop instead
- DPF cleaning — an ash-loaded filter has to come off and be cleaned on a machine or replaced; a regen can’t burn ash
- DOC or SCR catalyst replacement, depending on access and parts
- Engine problems causing the soot, like injector or turbo faults, may need shop time
- Emissions deletes or tampering — illegal under federal law, and not a repair
Repair it where it sits, or tow it?
Most aftertreatment problems can be diagnosed, and often fixed, on site. A loaded DPF that just needs a regen, a failed NOx or temperature sensor, or crystallized DEF in a dosing valve is standard mobile work.
A shop makes more sense when the DPF is full of ash and has to come off, when a regen fails because of an internal engine problem, or when the truck is too derated to reach a safe place to work. If it can still move at reduced speed, get it off the interstate to a truck stop or yard where a parked regen can run safely.
Have this ready when you call
A few details up front help the mechanic load the right parts and tools and get it done in one trip.
- Which lamps are on: DPF, high exhaust system temperature, DEF, check engine, or stop engine
- Whether the DPF lamp is solid or flashing
- How derated the truck is — full power, reduced power, or crawl speed
- Any recent DEF fill, especially from a jug or unfamiliar source
- When the last regen ran and whether a parked regen was tried
- Engine make and model
Makes & engines we work on
- Freightliner
- Peterbilt
- Kenworth
- Volvo
- Mack
- International
- Western Star
Class 6 through Class 8 trucks, including engines from Cummins, Detroit Diesel, PACCAR, Volvo, Mack, Navistar, and Caterpillar.
DPF, DEF & Regen Service around Knoxville & East Tennessee
Regen and DEF calls come from trucks that idle and creep: local delivery fleets in Knoxville, construction and dump trucks around new development in Blount and Loudon counties, and yard tractors at distribution centers. Highway trucks hit DEF derates too, often on a cold morning at a truck stop or on I-40 and I-75 when a sensor quits between towns.
Highways we cover
Towns we cover
- Knoxville
- Farragut
- Maryville & Alcoa
- Oak Ridge
- Clinton
- Lenoir City & Loudon
- Sevierville & Pigeon Forge
- Morristown
DPF, DEF & Regen Service: common questions
Can you run a forced regen on the side of the road?
Often, yes, if the truck is parked somewhere safe and the system allows it. A parked regen gets the exhaust very hot, so the truck needs to be away from dry grass, leaves, fuel spills, and anything that can burn. On a narrow shoulder, moving to a lot first is safer.
Why won’t my truck regen by itself?
Common causes are a failed differential pressure or exhaust temperature sensor, an exhaust leak, an EGR problem, or a duty cycle with so much idling and so many short trips that a regen never gets to finish.
What happens if I ignore a DEF warning?
Most trucks step down through harder and harder derates, and the last stage can hold the truck to crawl speed. Fixing it early is faster and cheaper.
Does cold weather cause DEF problems?
Yes. DEF freezes around 12°F. Trucks have heaters to thaw it, but a failed heater, line, or sensor often shows up on the first hard freeze. Keep jugs of DEF somewhere that doesn’t freeze solid.
Can a regen fix a DPF full of ash?
No. Regeneration burns soot, not ash. Ash builds over time, and eventually the filter has to come off to be cleaned or replaced.
Will you delete my DPF or DEF system?
No. Removing or disabling emissions equipment violates federal law and causes problems with inspections, resale, and warranty. We repair these systems.