The short answer
There is no single federal definition of a "PM service." 49 CFR 396.3 requires motor carriers to systematically inspect, repair and maintain their vehicles, but leaves the details to the carrier. In practice, most PM services combine two things: scheduled service (fluids, filters, lubrication) and a safety inspection. What goes into each depends on the engine and component manufacturers, the duty cycle and the fleet's history. See PM service.
Service levels: A, B and C
Many shops and fleets define service levels that build on each other. Names and contents vary, so treat this as a common pattern, not a standard:
A service (basic) - Chassis lubrication. - Check and top off engine oil, coolant, power steering fluid, windshield washer fluid. - Check belts and hoses. - Visual safety inspection: lights, tires, brakes, leaks. - Record mileage or hours and any defects.
B service (standard) - Everything in A. - Engine oil and filter change. - Fuel filters and water separator service. - Air dryer cartridge check or service, according to the manufacturer. - Full safety inspection with measurements, such as tread depth and brake pushrod stroke. - Battery and charging system test.
C service (major) - Everything in B. - Fluid changes on longer intervals, such as coolant, transmission and axle lubricants, according to manufacturer schedules. - Air filter replacement. - Valve adjustment and other engine tasks if due. - Aftertreatment inspection and service as the engine manufacturer specifies.
The fleet and shop should write down exactly what each level contains so every technician performs the same work.
The inspection systems to cover
Appendix A to 49 CFR Part 396 sets the minimum periodic inspection standards used for DOT annual inspections. Its list of systems is a sound base for any PM inspection:
- Brake system: service brakes, parking brake, brake drums or rotors, hoses and tubing, low air warning, tractor protection valve, air compressor, and brake adjustment.
- Coupling devices: fifth wheel, pintle hooks, drawbars, safety devices.
- Exhaust system: leaks and placement near fuel or wiring.
- Fuel system: visible leaks, fuel tank filler caps, fuel tanks securely attached.
- Lighting devices: all required lamps operative.
- Safe loading: protection against shifting cargo.
- Steering mechanism: steering wheel free play, steering column, gearbox, pitman arm, power steering, ball and socket joints, tie rods and drag links, nuts.
- Suspension: U-bolts, spring hangers, spring assemblies, torque and track components.
- Frame: cracks, loose or missing fasteners.
- Tires: tread depth, inflation, damage.
- Wheels and rims: lock or side rings, cracks, fasteners, welds.
- Windshield glazing and wipers.
Covering these on each PM means the truck is held to the same standard every time, and makes the annual inspection a confirmation instead of a surprise.
Measurements that matter
A PM is more useful when the technician records numbers, not just check marks. Common measurements include:
- Tire tread depth. 49 CFR 393.75 sets minimums: tires on the front steering axle of a power unit must have at least 4/32 inch of tread at any major tread groove, and other tires must have at least 2/32 inch. See tire tread depth.
- Brake pushrod stroke. 49 CFR 393.47 sets adjustment limits by chamber type. For a common type 30 standard stroke chamber, the limit is 2 inches. See brake chamber.
- Brake lining thickness and drum or rotor condition.
- Tire pressure, compared with the fleet's targets.
- Battery test results.
Recording numbers lets the fleet see wear trends and plan replacements before parts reach their limits.
Fluids and filters
The fluid and filter part of a PM follows the engine, transmission and axle manufacturer schedules. Intervals depend on engine model, oil specification, fuel use, idle time and duty. Some fleets use oil analysis to adjust intervals. The shop should record which fluids and filters were used, with part numbers and quantities, so the fleet can show what was done.
Defects found during the PM
PM inspections often find repairs. A clear process helps:
- Record the defect with a description, measurement and photo.
- Mark whether it is a safety item that must be fixed before the truck leaves. 49 CFR 396.7 says a motor vehicle must not be operated in a condition likely to cause an accident or a breakdown.
- Quote other repairs for approval or schedule them.
- Record the correction or the decision to defer.
What the fleet should get afterward
After a PM, the fleet should receive:
- The completed checklist with measurements.
- A list of services performed, with parts and fluids.
- Defects found and what was done about each one.
- The next due date or mileage.
This feeds the records required by 49 CFR 396.3(b): an identification of the vehicle, a means to indicate the nature and due date of inspection and maintenance operations, and a record of inspection, repairs and maintenance indicating their date and nature.
PM and the annual inspection
49 CFR 396.17 requires every commercial motor vehicle to be inspected at least once every 12 months. A PM can include the annual inspection if a qualified inspector performs it and the inspection meets Appendix A. Many fleets pair them to save downtime. See DOT annual inspection checklist.
Questions to ask a shop before booking
Because PM contents vary, ask the shop for a written list of what its service includes, which fluids and filters are covered, whether the safety inspection records measurements, how defects are reported and approved, and what records you will receive afterward.
Trailers
If the fleet runs trailers, they need their own PM program. Trailer PMs focus on brakes, tires, wheels, lights, suspension, landing gear, doors and the kingpin area, plus refrigeration units where present. Trailers are also subject to the annual inspection requirement.
Mobile PM services
Many PMs are now done at the fleet's yard by a mobile technician. The contents stay the same, but the planning changes. The technician needs the right filters and fluids for every unit on the route, a way to capture used oil and other fluids, and enough light and space to inspect the brakes and undercarriage safely. Some tasks, such as major fluid changes or repairs that need a lift, may still have to be scheduled at a shop. Agree with the fleet which service levels can be done on site and which cannot.
Setting up the program around the service
The PM itself is only one part of a working program. Someone has to track due dates, get the truck to the technician, follow up on defects and keep the records. See how to run a PM program for a fleet for the full process, and semi-truck PM service checklist for a detailed item-by-item list.
How to price a PM
Pricing varies widely by region, truck, service level and whether parts and fluids are included. Many shops publish a set price per service level plus fluids and filters at cost or at a markup, and quote repairs found during the PM separately. See PM service cost for a semi-truck.
How long a PM takes
Time depends on the service level, the truck and the shop. Rather than relying on general figures, track your own completed repair orders by service level and use those numbers when you quote and schedule.
How MetaFleet helps
MetaFleet supports preventive maintenance with reminders and digital inspections that capture measurements and photos, and work orders that turn found defects into quoted repairs. Get a walkthrough.