Heavy Truck PM Schedule Basics: A, B, and C Service Explained

Preventive maintenance on a Class 7 or 8 truck isn’t one big service — it’s a tiered schedule. Most fleets organize it as A, B, and C service, each more thorough than the last. Get the tiers right and you trade unplanned roadside breakdowns for planned shop time.

The three tiers

A Service — the frequent, light check. Typically every 10,000–15,000 miles or on a set time interval. Lube, oil and filter, and a walk-around inspection: lights, tires, leaks, fluid levels, belts, and brake-adjustment check.

B Service — everything in A, plus deeper items roughly every 2–3 A intervals: fuel filters, cabin/air filters, transmission and differential fluid checks, more detailed brake and suspension inspection.

C Service — the comprehensive annual-ish service: A and B items plus major fluid changes, cooling-system service, valve adjustment where applicable, and a full DOT-style inspection.

Tie it to the DOT inspection

Every commercial vehicle needs a federal annual inspection. The smart move is to line your C service up with it so the truck is already torn into and inspected on the same visit. That’s also when you catch the things that fail roadside inspections: brakes out of adjustment, air leaks, tire tread and sidewall issues, and lighting.

Aftertreatment and DEF

Modern heavy diesels live and die by their aftertreatment. Keep DEF topped with clean fluid, watch for derate warnings, and don’t ignore a check-engine light tied to the DPF or SCR system — a clogged particulate filter or a failed sensor can put the truck into a speed derate at the worst possible time.

Track it by engine hours and miles

Long-haul trucks rack up miles; vocational and port-drayage trucks rack up hours idling and in stop-and-go. If your trucks idle a lot — common around the Charleston port — schedule by engine hours, not just odometer, or you’ll under-service them.

A consistent PM program is the cheapest insurance a fleet can buy. Running several trucks and don’t want to manage it yourself? That’s exactly what a fleet-maintenance program is for.