40 CFR 205.160-4: -4 Testing procedures.

(a) The manufacturer must conduct one valid test in accordance with the appropriate test procedures specified in Appendix I, on each vehicle selected for testing under this subpart.

(b) In the event a vehicle is unable to complete the noise emission test, the manufacturer may replace the vehicle. Any replacement vehicle must be a production vehicle of the same category, configuration or subgroup as the vehicle which it replaced, and it is subject to all the provisions of this subpart.