1993 Buick Regal Owner's Manual - Page 273

The services shown in this schedule up to 48 000 miles (80 000 km) should be performed after 48 000 miles at the same intervals. * 3- The U.S. Environmental Protection Agency hasdetermined that the failure to perform this maintenance item will not nullify the emission warranty or limit recall liability prior to the compktion of vehicle useful life. General Motors, however, urges that all recommended maintenance services be performed at the indicated intervals and the maintenance be recorded in "Section EMaintenance Record". An Emission Control Service. 271