Except as specified in this section, the requirements of this subpart shall be applicable to all 1972 and later model year vehicles and engines. The requirement to report emission-related defects affecting a given class or category of vehicles or engines shall remain applicable for five years from the end of the model year in which such vehicles or engines were manufactured. Manufacturers of heavy-duty motor vehicle engines may comply with the defect reporting requirements of 40 CFR 1068.501 instead of the requirements of this subpart. [76 FR 57374, Sept. 15, 2011]