40 CFR § 91.806
Voluntary emissions recall
June 9, 2020
(a) Prior to an EPA ordered recall, the manufacturer may perform a voluntary emissions recall pursuant to regulations at §91.904 of this part. Such manufacturer is subject to the reporting requirements at §91.905 of this part.
(b) Once EPA determines that a substantial number of engines fail to conform with the requirements of section 213 of the Act or this part, the manufacturer will not have the option of a voluntary emissions recall.