Upgrade means to modify a locomotive or locomotive engine that was originally manufactured prior to January 1, 1973 (or a locomotive or locomotive engine that was originally manufactured on or after January 1, 1973, and that is not subject to the emission standards of this part), such that it is intended to comply with the Tier 0 standards. Upgrading is a type of remanufacturing.
40 CFR § 92.2
The definitions of this section apply to this subpart. They also apply to all subparts of this part, except where noted otherwise.