(g)(3) Except for air conditioning, where it is expected that 33 percent or less of a carline, within an engine-system combination, will be equipped with an item (whether that item is standard equipment or an option) that can reasonably be expected to influence emissions, that item may not be installed on any emission data vehicle or durability data vehicle of that carline within that engine-system combination, unless that item is standard equipment on that vehicle or specifically required by the Administrator.
40 C.F.R. §86.000-24