https://ww3.arb.ca.gov/msprog/truckstop/tb/truckbus.htm
Diesel trucks and buses with a Gross Vehicle Weight Rating(GVWR) that is greater than 14,001 pounds (lbs), must reduce exhaust emissions by meeting particulate matter (PM) filter requirements and upgrading to a 2010 or newer engine model year (EMY).
The Regulation applies to:
Diesel vehicles with a GVWR greater than 14,000 lbs.
Privately and federally owned trucks and buses that operate in California
Any person, business, school district, tribal reservation, or federal government agency that owns, operates, leases or rents affected vehicles.
The Regulation does not apply to:
Gasoline or dedicated natural gas vehicles
Solid Waste Collection Vehicles
Public Agency and Utility Vehicles (Not Federal)
Drayage (Port or Rail) Trucks
Transit/Urban Buses
Personal use motor homes or recreational vehicles