You can bring your US-registered vehicle into Mexico.

Mexico has two Free Zones - Baja and Sonora - in which US-registered vehicles may remain indefinitely, as long as their registration remains valid and current.

You can bring your US-registered vehicle into Mexico beyond the Free Zones, but only on a temporary basis.  You must secure a Temporary Import Permit for your vehicle, which is good for up to 180 days and stamped into your passport.

We strongly encourage following these steps before crossing borders south of the US.

If you sell your vehicle in Mexico, overstay your vehicle's Temporary Import Permit, or attempt to leave Mexico without your vehicle, Mexican customs authorities will assess an import tariff on your vehicle, the value of which can be large and arbitrary.

You must secure liability insurance for your vehicle before crossing into Mexico, as coverage under US auto policies only extends 25 miles into Mexico.

Each country south of Mexico maintains a temporary import process and requires liability insurance.  Each of these requirements may be secured at most border crossings.