issue a final rule requiring all new passenger motor vehicles weighing less than 10,000 pounds gross vehicle weight to be equipped with an alarm system to alert the operator to check rear designated seating positions after the vehicle motor or engine is deactivated by the operator. (b) Phase-In The rule issued pursuant to subsection (a) shall require full compliance with the rule beginning on September 1st of the calendar year that begins 2 years after the date on which the final rule is issued. (c) Definitions For purposes of this section— (1) the term passenger motor vehicle has the meaning given that term in section 32101