During the development and testing of the new M291 powerplant, it became apparent to Sauber Mercedes that there were problems in the engine design and construction. Thus the team started the 1991 season with a lone C291, while at the same time running an older C11.
During the development and testing of the new M291 powerplant, it became clear to Sauber Mercedes that there were issues in the engine design and construction. Thus, the team began the 1991 season with a single C291 car, while concurrently using an older C11.