40 CFR § 1037.655 - Post-useful life vehicle modifications.
(a) General. Vehicle modifications during and after the useful life are presumed to violate 42 U.S.C. 7522(a)(3)(A) if they involve removing or rendering inoperative any emission control device installed to comply with the requirements of this part 1037. This section specifies vehicle modifications that may occur in certain circumstances after a vehicle reaches the end of its regulatory useful life. EPA may require a higher burden of proof with respect to modifications that occur within the useful life period, and the specific examples presented here do not necessarily apply within the useful life. This section also does not apply with respect to engine modifications or recalibrations.
(b) Allowable modifications. You may modify a vehicle for the purpose of reducing emissions, provided you have a reasonable technical basis for knowing that such modification will not increase emissions of any other pollutant. “Reasonable technical basis” has the meaning given in 40 CFR 1068.30. This generally requires you to have information that would lead an engineer or other person familiar with engine and vehicle design and function to reasonably believe that the modifications will not increase emissions of any regulated pollutant.
(c) Examples of allowable modifications. The following are examples of allowable modifications:
(d) Examples of prohibited modifications. The following are examples of modifications that are not allowable: