Prototypes of gas sensitive Schottky diodes with a platinum gate electrode have been fabricated on monocrystalline 6H-SiC substrates and tested on petrol engines. The sensors are mounted in the housing and on the heater of HEGO sensors. The air/fuel ratio of each cylinder is individually controlled by UHEGO sensors. Three gas sensitive SiC diodes together with another UHEGO sensor, serving as the reference sensor, are mounted into the exhaust pipe. At the operating temperature used, around 600-800°C, the SiC sensors show a large variation of the output signal for small variations of the air/fuel ratio around the stoichiometric ratio. The response time of the sensor is small enough to detect the air/fuel ratio of individual cylinders. We show how the sensor can be used to detect misfire and/or individual cylinders that deviate from stoichiometry. The SiC sensor thus shows promising potential for cylinder selective and more effective combustion control.