Fleets schedule preventive maintenance by mileage, by engine hours, or by what inspections and data show. Most good programs use all three, because no single trigger fits every truck or every component. The real decision is which trigger runs which part of the plan, truck by truck, based on how each one is used.
Before picking triggers, it helps to know the baseline. FMCSA rule 49 CFR 396.3 requires every motor carrier to systematically inspect, repair and maintain the vehicles it controls. The carrier's records for each vehicle must include a way to show the nature and due date of inspection and maintenance work, and a record of the inspections, repairs and maintenance done. Those records have to be kept where the vehicle is housed or maintained for one year, and for six months after the vehicle leaves the carrier's control.
On top of that, each commercial vehicle in a combination, including trailers, must pass a periodic inspection at least once every 12 months, with documentation on the vehicle (49 CFR 396.17). And drivers must report defects at the end of each day's work (49 CFR 396.11).
The regulation does not tell you to use mileage or hours. It tells you to have a system and prove it. The three methods below are how fleets build that system.
Mileage is the easiest trigger to track and fits components that wear with distance: brakes, tires, wheel bearings, driveline parts and, for highway trucks, engine oil.
It works best for trucks that run steady, predictable routes. Our own service recommendations are mileage-based for several systems. We recommend checking the transmission and clutch every 12,500 miles and having the DPF system checked every 300,000 miles. Brake lining life varies by route; hard braking and town driving wear linings faster than long highway runs.
The weakness: mileage understates engine wear on trucks that spend a lot of time running while parked.
Engine hours fit trucks that run for long stretches without covering many miles: trucks that idle at job sites, run PTO equipment such as pumps or hydraulics, or idle for heat and air conditioning. On those trucks, the odometer says the engine has barely worked when it has been running all day.
Idle time is not free. The U.S. Department of Energy's Alternative Fuels Data Center notes that idling wastes fuel and increases engine wear, and that U.S. cars and trucks use more than 6 billion gallons of diesel and gasoline a year without moving. Many engine makers set oil change intervals in hours as well as miles for this reason, so check the maintenance manual for your engines and track whichever limit comes first.
For mixed fleets, pull engine hours from the engine control module or telematics at every service, not just mileage.
The third method schedules work based on what the truck shows you: driver reports, inspection findings, fault codes and oil analysis. It catches problems that arrive before any fixed interval, such as a leaking seal, a brake that has gone out of adjustment or coolant showing up in the oil.
This is the safety net behind the other two methods, and it is where the daily driver report earns its keep. Under 396.11, a defect a driver reports must be repaired, or certified as not needing repair, before the truck is driven again. A fleet that acts on those reports quickly turns small findings into scheduled work instead of roadside breakdowns. Regular inspections with good diagnostic equipment catch problems before they become extensive repairs and costly downtime.
A workable plan for most fleets looks like this:
Group the work so one shop visit covers several items. An oil service, brake check, tire check and walk-around in the same visit costs far less downtime than four separate trips.
Then review the plan. If a truck keeps coming in between services with the same problem, its interval or duty category is probably wrong.
Maintenance is a growing cost. The American Transportation Research Institute's 2026 operational cost analysis found that the industry-average cost to operate a truck reached a record $2.336 per mile in 2025, with repair and maintenance among the fastest-rising line items. A planned visit costs less than a breakdown, a tow and a missed delivery. A good maintenance program limits long-term maintenance costs and extends the life of trucks and equipment.
We service Class 4 to 8 trucks and trailers: PMs, inspections, brakes, tires and much more. We can set PM schedules around how each of your trucks actually runs, and we get the job done when we say it will be done. Our mobile units can also handle preventive maintenance and DOT inspections on site, so some trucks never have to leave your yard.
Statesville: 704-960-8951. Bessemer City (serving Gastonia and Gaston County): 980-391-4100. Monroe: 980-396-6750. You can also email marketing@gallaherfleetsolutions.com or request service at www.gallaherfleetsolutions.com/contact, and we will get back to you the same business day. See preventive maintenance for the full service.