No, you cannot legally enter Mexico by car without a valid passport. U.S. citizens driving into Mexico must present a valid passport book or a passport card. While a passport card is a cheaper, wallet-sized alternative to the book, it is only valid for land and sea travel to Canada, Mexico, the Caribbean, and Bermuda. The Western Hemisphere Travel Initiative (WHTI) governs these rules, and Mexican authorities strictly enforce them at border crossings.
Attempting to cross without proper documentation will result in being denied entry by Mexican immigration officials. Relying on a driver's license and birth certificate is no longer sufficient. While you can re-enter the United States at a land border crossing with a passport card or other WHTI-compliant documents like an Enhanced Driver's License (EDL), the U.S. Customs and Border Protection (CBP) officer will still question you, and not having a passport for the initial exit can complicate your return.
The process involves stopping at the Mexican immigration office located just after the border crossing. You must obtain a Tourist Permit (FMM), which may have a fee associated with it, especially if your stay is longer than seven days or you travel beyond the border zone. For this, your passport is essential. Driving a car also requires a temporary vehicle import permit if you plan to travel beyond the immediate border areas. The bottom line is that a passport is non-negotiable for a smooth and legal trip.
