This paper presents an implemented idea for gear shifting optimization with the aim of fuel consumption minimization. A new combined theoretical and experimental approach has been developed using the On-Board Diagnostic (OBD) technology which so far has not been used for this purpose. A matrix of driving modes according to which tests were performed is obtained and a special data acquisition system and analysis process have been developed. Functional relations between experimental test modes and adequate OBD parameters have been obtained and all necessary operations have been conducted to enable their use as inputs for the designed algorithm. The created model has been tested in real exploitation conditions on a passenger car.