There are essentially three sets of laws that apply to defective vehicles and products in the United States.
1. The Magnuson-Moss Warranty Act is a Federal Law that protects the buyer of any product that costs more than $25 and comes with an express written warranty. Here is a summary of the Act in layman's language, and here is a more detailed explanation of the Act from the FTC.
2. The Uniform Commercial Code or UCC has been adopted in all 50 states and covers contracts dealing with the sale of products.
3. Summary of State Lemon Laws here and individual State Lemon Laws begin here.