Not later than 12 months after
November 15, 1990, the Administrator shall revise the regulations promulgated under this subsection to add test procedures capable of determining whether model year 1994 and later model year light-duty vehicles and light-duty trucks, when properly maintained and used, will pass the inspection methods and procedures established under
section 7541(b) of this title for that model year, under conditions reasonably likely to be encountered in the conduct of inspection and maintenance programs, but which those programs cannot reasonably influence or control. The conditions shall include fuel characteristics, ambient temperature, and short (30 minutes or less) waiting periods before tests are conducted. The Administrator shall not grant a certificate of conformity under this subsection for any 1994 or later model year vehicle or engine that the Administrator concludes cannot pass the test procedures established under this paragraph.