Do you have to changed both cv joints when only one goes bad?

It's not strictly necessary to change both CV joints when only one fails, but doing so can be beneficial. Replacing only the damaged joint might save money initially, but if the other joint is old or has high mileage, it could fail soon after. Changing both can ensure consistent performance and avoid future repairs. Ultimately, the decision should consider the vehicle's age, mileage, and overall condition.