Abstract: An intake air pressure Pm downstream of a throttle valve of an internal combustion engine is estimated by computation from a basic fuel injection quantity Tp set for an intake air flow rate Q and an engine rotational speed Ne, an intake air temperature TA, and an intake air volumetric efficiency .eta., according to the equation Pm=C.multidot.Tp.multidot.TA/.eta.. The estimated intake air pressure Pm is then used in a fuel supply control system wherein the fuel injection pressure from a fuel injection valve is such that a differential pressure relative to atmospheric pressure is constant, to thereby correct the fuel injection period of the fuel injection valve. As a result, there is no requirement for a sensor for detecting intake air pressure. Moreover, since a reference pressure chamber of the pressure regulator can be opened to the atmosphere, piping can be shortened, enabling a more compact unit.

Abstract: A slip condition of a torque converter is learned at a predetermined operating condition with a lock-up mechanism disengaged, and a diagnosis condition (for example a start time or judgement level of the fault diagnosis) used in diagnosing a fault in the lock-up mechanism on the basis of slip conditions of the torque converter which change after issue of a disengage command to the lock-up mechanism, is corrected in accordance with the learned result. As a result, the diagnosis condition which is conventionally set assuming a maximum viscosity for the operating fluid, can be changed to correspond to the actual viscosity of the operating fluid being used.