40 CFR § 1048.425
What records must I keep?
June 9, 2020
(a) Organize and maintain your records as described in this section. We may review your records at any time.
(b) Keep paper records of your in-use testing for one full year after you complete all the testing required for an engine family in a model year. You may use any additional storage formats or media if you like.
(c) Keep a copy of the written reports described in §1048.420.
(d) Keep any additional records related to the procurement process.
[67 FR 68347, Nov. 8, 2002, as amended at 70 FR 40476, July 13, 2005]