1993 Buick Riviera Owner's Manual - Page 277
1993 Buick Riviera Manual
Page 277 highlights
The services shown inthis schedule upto 48 000 miles (80.000km) shouldbe performed after 000 miles at the same 48 * I An Emission Control Service. The U.S. Environmental Protection Agency has determined the failure to perform this maintenance item will not nullify the emission warranty recall liability prior to the completion that or limit of vehicle useful life. General Motors, however, urges all recommended maintenance services be performedthe indicated intervals and the maintenance that at be recorded in "Section E:Maintenance Record". 275