40 CFR §1045.425

1. (a)Organize and maintain your records as described in this section. We may review your records at any time, so it is important to keep required information readily available.
2. (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.
3. (c)Keep a copy of the written reports described in § 1045.420.
4. (d)Keep any additional records related to the procurement process.