This subpart applies to manufacturers of motor vehicles and motor vehicle engines (hereafter referred to as vehicles) which are subject to the requirements of title II of the Clean Air Act. This subpart applies to the following vehicles:
(a) 1968 and later model year light-duty vehicles and light-duty trucks.
(b) 1970 and later model year heavy-duty engines built after December 31, 1969.
(c) 1978 and later model year motorcycles built after December 31, 1977.
(d) References in this subpart to engine families and emission control systems shall be deemed to apply to durability groups and test groups as applicable for manufacturers certifying new light-duty vehicles, light-duty trucks, and Otto-cycle complete heavy-duty vehicles under the provisions of subpart S of this part.