40 CFR § 1051.650 - What special provisions apply for converting a vehicle to use an alternate fuel?
A certificate of conformity is no longer valid for a vehicle if the vehicle is modified such that it is not in a configuration covered by the certificate. This section applies if such modifications are done to convert the vehicle to run on a different fuel type. Such vehicles may be recertified as specified in this section if the original certificate is no longer valid for that vehicle.
(b) Converting a certified vehicle that is not new to run on a different fuel type violates 40 CFR 1068.101(b)(1) if the modified vehicle is not covered by a certificate of conformity. We may specify alternate certification provisions consistent with the requirements of this part. For example, you may certify the modified vehicle for a partial useful life. For example, if the vehicle is modified halfway through its original useful life period, you may generally certify the vehicle based on completing the original useful life period; or if the vehicle is modified after the original useful life period is past, you may generally certify the vehicle based on testing that does not involve further durability demonstration.
(c) Vehicles (or engines) may be certified using the certification procedures for new vehicles (or engines) as specified in this part or using the certification procedures for aftermarket parts as specified in 40 CFR part 85, subpart V. Unless the original vehicle manufacturer continues to be responsible for the vehicle as specified in paragraph (d) of this section, you must remove the original manufacturer's emission control information label if you recertify the vehicle.
(d) The original vehicle manufacturer is not responsible for operation of modified vehicles in configurations resulting from modifications performed by others. In cases where the modification allows a vehicle to be operated in either its original configuration or a modified configuration, the original vehicle manufacturer remains responsible for operation of the modified vehicle in its original configuration.