Method of detecting abnormality in a reference crank angle position

Abstract

A method of detecting abnormality in a reference crank angle position detection system of a control system for controlling an internal combustion engine, the control system using at least reference pulses generated, respectively, at predetermined crank angles of the crankshaft and detected by the detection system, and crank angle pulses generated, respectively, at predetermined angles of the crankshaft and with a pulse repetition period shorter than that of the reference pulses, for controlling the engine. Counting of crank angle pulses is started from the time each reference pulse is generated. It is determined whether or not one reference pulse has been generated between an immediately preceding crank angle pulse and a present one, when the counted value is equal to a predetermined value. If not, it is decided that abnormality exists in the occurrence of reference pulses. Alternatively, a number of times of execution of the above determination are counted when the determination result is negative, to decide that abnormality exists in the occurrence of reference pulses when the counting has been continually effected until the counted value reaches a predetermined value.