6. Cadillac STS
The Cadillac STS was built for 6 years, between 2005 and 20011. When it was released it garnered praise for its comfortable ride and great handling. It was offered with a choice of V-6 and V-8 engines, both of which are costly to repair when problems occur, and problems were common with this vehicle. The STS was given low marks for overall dependability by J.D. Power. Engine, transmission, electrical, and braking system problems are commonly reported problems for the STS. The fuel system, cooling system, and navigation system are also common problem areas. With so many problems and the cost to fix them being so high, the Cadillac STS is one of the worst used cars you can buy.