1985 Autocar: we work on any truck
If it runs diesel and needs help, we'll show up. Age is not a barrier: classic, vintage, or modern.
Commercial & Heavy-Duty Truck Repair
Mobile Commercial & Heavy-Duty Truck Repair in Charleston, SC. We Come to You.
On-site repair and diagnostics for the trucks businesses and fleets run: semis, tractor-trailers, box trucks, and work trucks, gas and diesel. We come to your yard, terminal, jobsite, or a truck-down roadside location, test the actual cause, and we do DOT inspections too. Running a mixed fleet with smaller vehicles? Ask us.
- Semis, tractor-trailers, box trucks, work trucks (gas and diesel, ¾-ton and up)
- Air brakes, aftertreatment, electrical, cooling, suspension, and DOT inspections
- Charleston, North Charleston, Summerville, Goose Creek, Mount Pleasant
Heavy-Duty Systems We Repair
Commercial truck systems handled on-site
Air brakes & air system
Brake chambers, slack adjusters, S-cams, valves, air compressor, air dryer, governor, and leak-down faults tested and repaired where the truck sits.
Aftertreatment & derate
DPF, DEF, SCR, and NOx faults, failed regens, and speed derates diagnosed to clear the fault and keep the truck legal and moving.
Electrical & no-start
Batteries, starters, alternators, grounds, corroded connectors, and sensor and wiring faults traced on heavy-duty and medium-duty trucks.
Cooling systems
Overheating, coolant leaks, water pumps, thermostats, radiators, fan clutches, and EGR-related cooling faults checked before a costly failure.
Suspension, airbags & wheel seals
Air ride and airbags, leveling valves, ride height, U-bolts, and leaking wheel seals and hubs inspected and serviced on-site.
Charging & batteries
Charging output, voltage drop, battery banks, and parasitic draw tested so your trucks start reliably on every shift.
DOT Compliance
DOT inspections & compliance: we keep you legal
Keeping a commercial truck in service means keeping it compliant. We perform the DOT annual inspection to the FMCSA 396.17 standard, walk the unit through inspection prep and pre-trip so it passes the first time, and get your inspection sticker applied. It is one less thing pulling your trucks out of service.
DOT annual inspection (396.17)
Full annual inspection to the federal 396.17 standard on tractors, trailers, box trucks, and work trucks, documented for your records.
Inspection prep & pre-trip
We pre-check the unit against the DOT criteria and fix what would fail before the inspection, so you avoid an out-of-service surprise.
Brake, lighting & air-system checks
Brake adjustment and components, lamps and reflectors, air-system integrity, and steering and chassis items verified to the DOT list.
Inspection sticker & compliance
Pass and we apply your inspection sticker and paperwork, keeping your unit and your fleet compliant and road-ready.
Need the details? See our DOT annual inspection and DOT inspection prep pages.
Engine Platforms
Heavy- and medium-duty engines we diagnose
Detroit DD13 / DD15
Aftertreatment and DEF faults, sensor and EGR issues, coolant and oil concerns, and no-start diagnostics on Detroit heavy-duty engines.
Cummins ISX / X15 & ISB
ISX and X15 derates, EGR and aftertreatment faults, injector and fuel concerns, plus medium-duty ISB and 6.7 troubleshooting.
PACCAR MX
MX-13 and MX-11 aftertreatment, DEF dosing, EGR, and electronic faults on Kenworth and Peterbilt trucks diagnosed on-site.
International (MaxxForce / A26)
MaxxForce and A26 emissions, EGR, turbo, and electrical faults sorted out where the truck is parked.
Medium-duty Isuzu & Hino
Isuzu N-series and Hino box trucks: regen and DPF faults, no-start, sensors, and PM for delivery and vocational units.
Work-truck gas & diesel
¾-ton and up gas and diesel work trucks and vans: diagnostics, electrical, cooling, and driveability on the units your business runs.
Roadside & Fleet
Truck-down support and small-fleet PM
A commercial truck sitting on the shoulder or stuck in your yard is lost revenue and a missed load. We bring the diagnostic equipment to the truck for roadside breakdowns and yard-down units, work the fault systematically, and get you a clear answer: repaired on-site when it is practical, or a clear direction before you lose more time.
For businesses running a handful of trucks, we set up preventive maintenance programs that keep units compliant and head off the breakdown before it strands a driver. Repeat and fleet customers get priority scheduling.
Why fleets & owners call us
- Mobile service where the truck is sitting
- DOT inspections and compliance handled on-site
- Testing before parts on heavy- and medium-duty trucks
- Roadside and yard-down truck support
- Small-fleet PM programs and priority scheduling
Commercial Truck Services
What we do for commercial trucks & fleets
DOT annual inspections
Federal 396.17 annual inspections, pre-trip and inspection prep, and inspection stickers to keep your units compliant.
Air brake service
Brake chambers, valves, slack adjusters, S-cams, compressor and dryer service, and air-system leak diagnosis.
Aftertreatment & emissions
DPF, DEF, SCR, and EGR faults, failed regens, and derates diagnosed and cleared to keep trucks legal.
Electrical & no-start
Batteries, starters, alternators, grounds, wiring, and sensor faults on heavy- and medium-duty trucks.
Preventive maintenance
Scheduled PM services, fluids and filters, and fleet inspection programs to head off breakdowns.
Roadside / breakdown
On-site roadside and yard-down support to get stranded commercial trucks diagnosed and moving.
Trailer repair
Trailer lights and wiring, brakes and ABS, air lines, and DOT items on dry vans, reefers, and flatbeds.
Cooling & charging
Overheating and coolant leaks, water pumps and thermostats, plus charging-system and battery diagnosis.
Need commercial or heavy-duty truck service in Charleston?
Call or text Lowcountry Diagnostics for on-site repair, fleet support, and DOT inspections. We come to the truck.
Commercial & DOT truck repair questions
What kinds of commercial trucks do you work on?
Semis, tractor-trailers, box trucks, and work trucks that businesses and fleets run (gas and diesel, ¾-ton and up). We handle heavy-duty and medium-duty makes and engines on-site. Running a mixed fleet with smaller vehicles too? Ask us.
Do you perform DOT annual inspections?
Yes. We perform DOT annual inspections to the FMCSA 396.17 standard, check brakes, lighting, air system, and steering, and get your unit its inspection sticker so you stay compliant. We also handle pre-trip and inspection prep.
Can you come to our yard or a truck stuck on the road?
Yes. We are mobile and come to your yard, terminal, jobsite, or a truck-down roadside location across the Charleston area. We test the actual cause where the truck sits so you avoid an unnecessary tow.
Do you support small fleets and owner-operators?
Yes. We support owner-operators and small fleets with roadside breakdown help, preventive maintenance programs, and priority scheduling to keep your trucks compliant and moving. Call or text (843) 310-0995.
Request Commercial Truck Service
Tell us where the truck is and what it is doing. For urgent truck-down calls or a DOT due today, calling or texting is fastest.
Urgent breakdown? Call or text (843) 310-0995 now.
Recent Repair Photos
A look at the repairs we make
Real field photos from Lowcountry Diagnostics, from engine diagnostics and electrical to hydraulic, HVAC, and heavy-duty truck service, handled on-site across the Charleston area.
Reviews
What Charleston truck owners and fleets say
“Joseph and team are top-notch! One of my fleet trucks went down and within the hour they had us back up and operational.”
“Great team, personal and professional. These men were responsive and had great diagnostic equipment paired with experience…”