(a) Prior to an EPA ordered recall, the manufacturer may perform a voluntary emissions recall pursuant to regulations at Sec. 91.904 of this part. Such manufacturer is subject to the reporting requirements at Sec. 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.