LED bulbs might not work in your car if the stock headlight reflectors of your car are designed for a specific type of bulb. If you swap out your halogen bulbs for LED bulbs without making any other modifications, the reflector could create a light band that is too narrow or too wide. This doesn’t necessarily mean you can’t use LED headlights in your car, but you might need to consider getting a whole new headlight housing in order to create a beam that is safe and legal.