40 CFR § 85.1804 - Approval of Plan: Implementation.
(a) If the Administrator finds that the remedial plan is designed and effective to correct the nonconformity, he will so notify the manufacturer in writing. If the remedial plan is not approved, the Administrator will provide the manufacturer notice of the disapproval and the reasons for the disapproval in writing.
(b) Upon receipt of notice from the Administrator that the remedial plan has been approved, the manufacturer shall commence implementation of the approved plan. Notification of vehicle or engine owners shall be in accordance with requirements of this subpart and shall proceed as follows:
(1) When no public hearing as described in § 85.1807 is requested by the manufacturer, notification of vehicles or engine owners shall commence within 15 working days of the receipt by the manufacturer of the Administrator's approval unless otherwise specified by the Administrator.
(2) When a public hearing as described in § 85.1807 is held, unless as a result of such hearing the Administrator withdraws the determination of nonconformity, the Administrator shall, within 60 days after the completion of such hearing, order the manufacturer to provide prompt notification of such nonconformity.