Diesel Repair Q&A for Drivers
The questions drivers and fleet managers actually ask — about roadside breakdowns, DPF fault codes, preventive maintenance, and commercial tires — answered by the diesel technicians who fix these trucks every day across Colorado, Wyoming, and Texas.
Emergency
What to do and who to call when a semi is down on the highway.
What should I do if my semi breaks down on I-70?
Get fully onto the shoulder, right of the fog line if you can safely move. Turn on your hazard lights, set out triangles or flares, and stay in the cab with your seatbelt on — do not work in traffic. Then call MTG Shops dispatch at (303) 476-3622 with your mile marker and direction of travel. We roll a mobile diesel mechanic to your mile marker, and most I-70 Colorado breakdowns are fixed on the shoulder without a tow.
Who provides 24-hour mobile truck repair in Colorado?
MTG Shops runs 24/7/365 mobile diesel mechanics across Colorado — I-70, I-76, I-25, the Front Range, and the eastern plains, run out of our Brush shop and mobile units. Dispatch is answered live every hour. Call (303) 476-3622 and give your mile marker and direction of travel.
Can a mobile mechanic repair my semi on the highway?
Yes. Our mobile units carry diagnostic laptops, an on-board air compressor, a welder, tire service gear, and common parts so a semi can be repaired on the shoulder — brakes, air systems, electrical, cooling, DPF/regen, tires, and no-starts. Most roadside calls are fixed on scene without a tow; if a bay is needed we tow to the nearest MTG shop.
What information should I give a truck repair dispatcher?
Your mile marker and direction of travel (or nearest exit / cross street), the interstate or highway name, the truck make / model / year, the symptom in your own words, your name and a call-back number that stays on, your company name and DOT number if applicable, and whether you are safely off the travel lane. The more we know, the faster the right tech and parts roll.
How quickly can mobile truck repair respond?
Dispatch is answered live 24/7/365. We give you an honest ETA on the call based on your mile marker and the nearest mobile unit. Most Colorado, Wyoming, and Texas calls are reached the same day, often fixed on scene within the hour of arrival depending on distance and the repair. We never quote a generic window — we tell you the real drive time.
Diagnostics
Fault codes, regens, and power loss — explained by working diesel techs.
What does a DPF fault code mean?
A DPF (diesel particulate filter) code means soot loading or an aftertreatment fault has triggered a warning or derate. It can mean the filter needs a parked or forced regen, a sensor failed (DPF differential pressure, NOx, exhaust gas temperature), or DOC efficiency dropped. We read the code on-truck with diagnostic laptops and tell you the real cause before recommending parts — we don't just clear it.
What happens during a diesel truck diagnostic?
A tech connects diagnostic laptops for Detroit, Cummins, Paccar, and Volvo, pulls active and inactive fault codes, and watches live data parameters (boost, EGT, NOx, fuel pressure, DPF load). We verify the circuit — sensor, harness, actuator, or mechanical — and road-test or replicate the fault before recommending a repair. You get the root cause, not a guess.
Can you perform a forced DPF regeneration?
Yes. We perform forced and parked DPF regens roadside and in-shop using on-truck service tools. If a regen won't complete, we diagnose why — DOC health, doser valve, NOx sensors, or a restricted DPF — before it becomes a derate that shuts you down. We carry the aftertreatment service tools to do this on the highway.
Why is my semi losing power?
Common causes are a derate from aftertreatment, DPF, or NOx faults; a boost or charge-air leak; clogged fuel or air filters; EGR issues; fuel restriction; or a sensor out of range (MAP, EGT, NOx). We pull codes and live data to isolate which one rather than swapping parts. Power loss that returns after a restart is usually an active derate — call before it hard-faults.
Maintenance
PM intervals, service scope, and pre-trip inspection guidance.
How often should a commercial truck receive preventive maintenance?
Most fleets run PM A (minor) every 10,000–15,000 miles and PM B (major) every 25,000–30,000 miles or quarterly, plus an annual DOT inspection. Severe duty — mountain grades, stop-and-go, high-idle — shortens those intervals. We tailor PM intervals to your operation and log every service so DOT audits are clean.
What is included in a semi-truck PM service?
A PM A covers engine oil and filter, fuel filters, air filter, grease chassis and driveline, and a full inspection of brakes / slack adjusters / drums, tires and wheel ends, suspension, steering, coolant and DPF/DEF levels, belts, hoses, and lights. PM B adds deeper drivetrain inspection and brake component teardowns. We use the inspection to flag roadside-fail items before they break.
What should fleets inspect before sending a truck out?
Pre-trip walk-around: lights and reflectors, tire condition and pressure, brakes and air system, fifth wheel and coupling, gladhands and air lines, fluid levels, belts and hoses, windshield and wipers, and all open DVIR items. A clean, documented pre-trip catches most roadside-fail defects — and most breakdowns — before the truck leaves the yard.
Tires
Commercial tire service, roadside replacement, and national accounts.
Where can I get semi-truck tires near Denver?
MTG Shops runs mobile tire service into the Denver area from our Brush shop and mobile units. We stock Ironman commercial tires — drive, steer, trailer, and mixed-service positions — and come to your truck or yard. No tow needed for a roadside tire. Call (303) 476-3622 with your position and size.
Does MTG service commercial truck tires?
Yes. We stock and service Ironman commercial tires across drive, steer, trailer, and mixed-service positions at our shops and on our mobile units. We handle roadside replacement, on-truck service, and wheel-end work — ironman GEN 2 I-28D drive, I-52A steer/all-position, I-48T trailer, and I-31M mixed service.
Does MTG accept Michelin national accounts?
We honor national-account tire programs where applicable. Bring your account details and we'll confirm fitment and on-hand inventory with dispatch. Our primary commercial tire line is Ironman, which we stock deeply — contact (303) 476-3622 to confirm account coverage and pricing for your fleet.
Call a diesel tech, not a script.
Dispatch answered live 24/7/365.