Abnormality detecting apparatus for means for sensing operating parameters of an internal combustion engine

An abnormality detecting apparatus for detecting abnormality in operating parameter sensing means for sensing the value of an operating parameter of an internal combustion engine in synchronism with generation of pulses of a signal indicative of predetermined rotational angle positions of said engine, said apparatus comprising:

• comparator means for determining whether or not the detected value of said operating parameter lies outside a predetermined range which is a normal range of output of said operating parameter sensing means, that is capable of being produced when said engine is operating in a normal state;
• first timer means responsive to results of said determination by said comparator means for measuring, when the detected value of said operating parameter lies outside said predetermined range, time elapsed from the instant at which the detected value of said operating parameter falls outside said predetermined range;
• decision means for deciding that said operating parameter sensing means is faulty when the elapsed time measured by said first timer means exceeds a first predetermined period of time;
• and
• second timer means disposed to be reset each time a pulse of said signal is generated for measuring time elapsed from the instant at which it becomes reset;
• said second timer means being adapted to halt the measuring operation of said first timer means when the elapsed time measured by said second timer means reaches a second predetermined period of time which is shorter than said first predetermined period of time, whereby the detection of abnormality in said operating parameter sensing means is interrupted.