General Motors recommends following the factory maintenance schedule for the 2002 GMC Sierra. The manual specifies four special services at 100,000 miles. If you've recently acquired your 2002 GMC Sierra, consider performing other services as well, such as an oil and filter change, as well as an air filter change, particularly if you do not know when the basic items were last serviced.
The estimated life for the 2002 Sierra's spark plugs and wires is approximately 100,000 miles, so the plugs and wires should be inspected and replaced if necessary at that mileage point. Over time, the wires degrade due to exposure to heat and the elements. This can cause them to develop a short, which would limit their effectiveness. Inspecting and replacing the spark plugs and wires if necessary ensures your Sierra continues to start and run efficiently.
The largest service required for the 2002 GMC Sierra at the 100,000 mile service interval is related to the truck's transmission. The automatic transmission should be flushed and the fluid should be changed by an authorized GMC dealer or a certified transmission specialist. Additionally, the transmission filter should be replaced.
Some four-wheel drive Sierras have an automatic transfer case. To determine if your four-wheel drive Sierra has an automatic or manual transfer case, look for the four-wheel drive selector. The automatic transfer case uses a button, usually located to the left of the steering wheel. For Sierras with a manual transfer case, the four-wheel drive selector is a traditional-looking gear shift in the center of the front floorboard. The automatic transfer case fluid should be replaced at 100,000 miles; the manual transfer case does not require service at this interval.
The Positive Crankcase Ventilation (PCV) valve should be inspected by a professional at 100,000 miles, and replaced if necessary. The PCV is an emission control device. If it's faulty, your Sierra's efficiency may be hindered.
