When a semi breaks down, get the truck as far off the road as possible, turn on the hazard flashers, put out your reflective warning triangles as federal rules require, and call your dispatch or a mobile diesel mechanic. Many roadside problems, such as air leaks, electrical faults, belts, hoses, tires, batteries, sensors and some fuel issues, can be fixed on the spot by a service truck, saving a heavy tow.
Safety first
Pull as far onto the shoulder as you safely can, away from curves and hills.
Hazard flashers on right away.
Place your reflective triangles as required by federal motor carrier safety rules (FMCSA), within the time limit and at the distances the rules set for your type of road.
Wear a high-visibility vest when outside the cab.
If the truck is in a dangerous spot or anyone is hurt, call 911.
What a roadside diesel mechanic can fix
- Air system: leaking lines, gladhands, brake chambers, compressor problems
- Electrical: lights, wiring, fuses, alternators, batteries, ABS faults
- Belts and hoses: cooling hoses, fan belts
- Fuel: filters, water separators, lift pumps, air in the system
- Aftertreatment: sensor faults and derates. See DPF and DEF problems
- Brakes: adjustment, chambers, some component replacement
- Tires: if the service offers tire work
Some repairs (major engine or transmission work, big parts not on the truck) need a tow to a shop. A good roadside mechanic tells you quickly.
What to tell the mechanic
- Exact location: highway, direction, mile marker, nearest exit
- Tractor and trailer details: year, make, engine, trailer type
- The fault: what happened, warning lights, codes
- Whether you're loaded and any hazmat placards
- Payment details: company account, fleet card, or pay on site
Keep downtime short
- Carry spare fuses, bulbs, gladhand seals and a basic tool kit
- Keep fault codes and recent repair history handy
- Have a list of mobile diesel mechanics along your regular routes. The directory's mobile diesel mechanic listings are sorted by state and city
- Stay on top of preventive maintenance. Many roadside failures show warning signs first
Night and weekend breakdowns
Many diesel road services run around the clock. See our guide to 24-hour mobile mechanics for what to expect after hours, and our general breakdown guide for the basics.
Frequently asked questions
How long does a roadside truck repair take?
Simple fixes like an air line or a belt may take an hour or two. Diagnostics and parts can stretch it.
Who pays for roadside service?
Usually the carrier or owner-operator. Fleet accounts and fleet cards are common.
Can a mobile mechanic help with a derate?
Often. They scan the codes, fix the cause if possible, and run a regen if needed.
Find a roadside diesel mechanic
See mobile diesel mechanics by state, or read our guide to mobile diesel mechanics.
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