In February 1934, the sedan was joined by the release of a convertible sedan. As the successor to the BMW 3/20 PS, the convertible adopted the technically advanced tubular frame of the BMW 303 and combined it with the revised four-cylinder engine of the BMW 3/20 PS. By comparison with the predecessor, the bore was increased by 2 mm in the BMW 309 in order to create rather more displacement and thereby generate more power. A total of 1,456 convertible sedans were produced by the time production came to an end in October 1935.