Pursuant to the EPA's Significant New Alternatives Policy program, this action lists the refrigerant 2,3,3,3-tetrafluoroprop-1- ene, also known as HFO-1234yf or R-1234yf, as acceptable, subject to use conditions, in the motor vehicle air conditioning end-use for certain types of newly manufactured nonroad (also called off-road) vehicles, which includes some vehicles that are also considered heavy- duty vehicles. EPA is also adopting the current versions of the industry safety standards SAE J639, SAE J1739, and SAE J2844 by incorporating them by reference into the use conditions for the listings in nonroad vehicles and previous listings for certain onroad vehicles covered in final rules issued separately in March 2011 and December 2016. In addition, EPA is requiring unique servicing fittings for use with small refrigerant cans (two pounds or less) of 2,3,3,3- tetrafluoroprop-1-ene that are used to service onroad and nonroad vehicles. Finally, EPA is adding a reference to the Agency's regulations under the Toxic Substances Control Act for 2,3,3,3- tetrafluoroprop-1-ene for the listings in nonroad vehicles and previous listings for certain onroad vehicles.