The definitions provided by this subpart are effective February 23, 1995 and apply to all motor vehicles regulated under 40 CFR part 86, subpart S, and to highway motorcycles regulated under 40 CFR part 86, subparts E and F. The definitions and related provisions in 40 CFR parts 1036, 1037, and 1068 apply instead of the provisions in this subpart for heavy-duty motor vehicles and heavy-duty motor vehicle engines regulated under 40 CFR part 86, subpart A, and 40 CFR parts 1036 and 1037.