40 CFR 91.804 - Maintenance, procurement and testing of in-use engines.
(a) A test engine must have a maintenance and use history representative of actual in-use conditions.
(1) To comply with this requirement a manufacturer must obtain information from the end users regarding the accumulated usage, maintenance, operating conditions, and storage of the test engines.
(2) Documents used in the procurement process must be maintained as required in § 91.121.
(b) The manufacturer may perform minimal set-to-spec maintenance on components of a test engine that are not subject to parameter adjustment. Maintenance may include only that which is listed in the owner's instructions for engines with the amount of service and age of the acquired test engine. Documentation of all maintenance and adjustments shall be maintained and retained as required by § 91.121.
(c) At least one valid emission test, according to the test procedure outlined in subpart E of this part, is required for each in-use engine.
(d) The Administrator may waive portions or requirements of the test procedure, if any, that are not necessary to determine in-use compliance.
(e) If a selected in-use engine fails to comply with any applicable emission standards, the manufacturer shall determine the reason for noncompliance. The manufacturer must report all such reasons of noncompliance within fifteen days of completion of testing.