Section 205.171-6 - Testing procedures(a) The manufacturer of the exhaust system must conduct one valid test in accordance with the appropriate test procedure specified in appendix I for each exhaust system selected for testing under this subpart.(b) No maintenance may be performed on the test exhaust system except as provided by § 205.171-2 . In the event an exhaust system is unable to complete the noise emission test, the manufacturer may replace the exhaust system. Any replacement exhaust system must be a production exhaust system of the same category as the exhaust system which it replaced, and it is subject to all the provisions of this subpart.45 FR 86718, Dec. 31, 1980, as amended at 47 FR 57723, Dec. 28, 1982