A Combustion Pressure Sensor (CPS) has been developed to measure combustion pressure in an engine cylinder. The CPS has been installed in the advanced TOYOTA lean burn engine for a Japanese commercial car on Oct. 1992. The control system with the CPS is useful for improvement of fuel consumption efficiency and emission of the commercial car.The CPS was installed in the first cylinder of the engine and measures the combustion pressure. In this system, the engine torque caused by a cycle combustion was calculated with the pressure signal of the sensor in real time. The sensor was especially designed to detect the lean burn limit with torque variations by means of unstable combustions.The CPS for the lean burn control system realizes advanced performances, durability, reliability, with the minimum components and the reasonable cost. This paper shows the structure and characteristics of the CPS, in detail.