A system consisting of an internal combustion engine (ICE) directly coupled to a permanent magnet synchronous machine (PMSM) is considered, which can be used as a range extender in hybrid electric vehicles (HEV) or as a power unit. For control of both, the synchronous machine and the engine, it is necessary to know the position of the rotor / crankshaft. Instead of using a position sensor, the position will be determined indirectly by using only electric variables of the PMSM by a self-sensing method. In general the angle determined in this way is only used for the field orientation and speed control of the PMSM. In this paper it is shown that it can be also used to control the ICE. Therefore, the electric angle has to be transformed to an absolute angle of the ICE relative to the top dead centre (TDC). This angle can be used to set the ignition point, control the timing of the valves and the injection. To transform the electric angle to an absolute angle, the ICE is used as a sensor to determine the TDC. Therefore the compression torque of the ICE is estimated through the PMSM and compared with an ideal model. The resulting benefit of the proposal is that the TDC can be obtained sensorless, with an accuracy of +/- 0.8 degrees.