GMC C series 2002 Owner's Manual page 305

(44) = Air brake service: Remove, disassemble, clean
and inspect the safety valve, standard brake chamber,
quick release valve, quick release/double check valve
combination, parking brake control valve, double check
valve, pressure protection valve and alcohol injector.
Remove, disassemble and clean the application valve;
replace parts showing wear. Remove, disassemble,
clean and inspect the spring brake control valve;
replace rubber parts.
(46) = Tighten the wheel stud nuts to the specified
torque values at 1,000 miles (1 600 km). Thereafter,
tighten them 1,000 miles (1 600 km) after each time
the wheel is removed. See "Tightening the Wheel Nuts"
in the Index.
7-24
(47) = Service is required now if you operate under any
of these Short Trip/City conditions:
D
Most trips are less than 5 to 10 miles (8 to 16 km).
This is particularly important when outside
temperatures are below freezing.
D
Most trips are through dusty areas.
D
You frequently tow a trailer.
D
The vehicle is operated at or near maximum
GVW ratings.
D
The vehicle is operated in hilly or
mountainous terrain.
(48) = Service is required now for all vehicles that have
not previously required service under the Short
Trip/City conditions.