Importance of PM Schedules A,B,C & D

  • Jan 14, 2020
  • Kunal Desai

Preventive maintenance (PM) is the key to any successful maintenance program for commercial motor vehicles. Through preventive maintenance, vehicles are inspected, repaired, and maintained in such a way that defects are prevented from surfacing in the first place, before a violation or accident can occur.

If vehicles are only brought into the shop when they need something, the program is not preventive, it is reactionary. The problem with reactionary maintenance programs is that they are based on failure, i.e., you notice something has failed and you fix it. This type of maintenance program is destined to lead to down-time and the resulting costs of idle equipment.

A preventive maintenance program, on the other hand, brings vehicles in for inspection and maintenance on a schedule, and repairs any items that are at, or even approaching, an established cut-off point. This allows you to make repairs on your schedule, prevent violations and accidents, and keep the vehicles rolling.

Preventive maintenance is also an attitude, a commitment. It means being constantly on the lookout for things that might go wrong. It means getting the best, most cost-effective equipment for the truck and then taking care of it. This is much like preventive medicine that stresses good eating habits and regular exercise as a continuing prescription for good health and long life.

The PM philosophy is widely used, not only because it reflects a modern attitude of conservation — of using assets wisely — but because it saves money. No one can argue with the bottom line. As PM takes hold, the standard of excellence for a maintenance shop changes from getting the fastest repairs to getting the fewest repairs.

Note that the federal regulations require a “systematic” inspection, repair, and maintenance program, but they leave the details up to you.

PM schedules

The actual maintenance portion of PM is composed of scheduled and standardized inspections and maintenance. This is sometimes referred to as the vehicles’ “scheduled service,” or simply “service.” PM services are commonly designated as A, B, C, D, etc. As you move down the alphabet from A to B and so on, the PM service (and time required) increases in complexity.

PM A service is also known as a “maintenance check-out” or “safety inspection” and generally consists of a safety check and lubrication as well as checks of key components such as brakes, lights, tire condition and inflation, and fluids. It also includes checking and adjusting high-wear components. The normal interval for “A” service is between 1,500 and 2,500 miles on light vehicles, and between 5,000 and 10,000 miles on medium- and heavy-duty vehicles.

Typically, these PM As are scheduled at half of the oil change interval of the vehicle.

Note: Some companies use an “inspection lane” and perform an “A” service every time the vehicle returns to the maintenance facility.

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PM B normally include all PM A items, and also include an oil and filter change as well as more in-depth checks of the engine and driveline. The normal interval for “B” service is 3,000 to 5,000 for light-duty vehicles and 10,000 to 20,000 for medium- and heavyduty vehicles. A PM B should also include a download of the ECM and action on any trouble codes or problems reported by the ECM (if applicable).

PM C service calls for both PM A and PM B service and more extensive service (i.e. alignment, scheduled component replacement, DOT annual inspection, and other scheduled engine and driveline component inspection or replacement). Normally, “C” services are scheduled annually. To make sure they are done in a timely manner, it is not unusual for carriers to actually schedule them at an 11-month interval.

PM D service is either a scheduled rebuild or replacement of a major component (e.g., engine, transmission, axle) or a “special” service. Examples of “special service” are seasonal service (winterization or summerization) and scheduled upgrade services. Scheduling of D services varies by company. The “D” designation may or may not be used, depending on the company.

Companies continue the lettering system based on their needs. Some companies go as far as PM L.

Trailer inspections

It’s important to remember to establish a PM schedule for trailers as well as power units. Trailers should be subject to the same PM program as trucks. Typical preventive maintenance scheduling for a trailer is:

T1 or TA services are scheduled every 3 months. This PM service includes an inspection and lubrication, including a check of (at a minimum) the lights, tires, brakes, coupling devices, safety equipment, and any other “systems” (refrigeration unit, sliding axles, etc.).

T2 or TB PMs are scheduled every six months. This PM service includes all the items of a T1 and a more in-depth inspection, as well as additional maintenance (pulling off hubcaps to check grease condition, retorquing lugs, etc.).

T3 or TC services are normally scheduled annually. These include all the inspection and maintenance included in a T1 and T2 service, along with more extensive maintenance such as an alignment or complete brake overhaul. Some carriers will also perform the periodic (annual) inspection required under §396.17 as part of the Type T3 service.

Don't forget the auxiliaries! Auxiliary power units (APUs), refrigeration units, wet kits, hydraulic pony engines, and idle reduction equipment all need to undergo the same scheduling process as the vehicles and trailers. The maintenance scheduling for these units can be rolled into the vehicle they are associated with. Examples would be servicing the wet kit on a vehicle each time the vehicle is serviced and servicing an APU as part of an annual inspection.

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