(a) Use of special test procedures by EPA. The Administrator may establish special test procedures for any engine that the Administrator determines is not susceptible to satisfactory testing under the specified test procedures set forth in subpart E of this part.

(b)(1) Use of alternate test procedures by an engine manufacturer. A manufacturer may elect to use an alternate test procedure provided that it yields results equal to the results from the specified test procedure in subpart E, its use is approved in advance by the Administrator, and the basis for equivalent results with the specified test procedure is fully described in the manufacturer's application.

(2) An engine manufacturer electing to use alternate test procedures is solely responsible for the results obtained. The Administrator may reject data generated under test procedures which do not correlate with data generated under the specified procedures.

(3) [Reserved]

(4) Where we specify mandatory compliance with the procedures of 40 CFR part 1065, manufacturers may elect to use the procedures specified in 40 CFR part 86, subpart N, as an alternate test procedure without advance approval by the Administrator.

(c) Optional procedures approved during Phase 1 can be carried over to Phase 2, following advance approval by the Administrator, to the extent the alternate procedure continues to yield results equal to the results from the specified test procedures in subpart E of this part.