System for diagnosing an internal combustion engine

Claim 1

In a system for diagnosing an internal combustion engine having a starter and a starter switch effective to produce a starter signal dependent on the operation of the starter switch, and first means for generating an engine speed signal dependent on engine speed, the improvement comprising a first comparator responsive to the engine speed signal for detecting the engine speed during cranking of the engine and producing a cranking signal; starter operation diagnosing circuit means responsive to the starter signal of said starter switch for producing a failure output when an absence of the starter signal during a presence of the cranking signal continues for a predetermined period; a second comparator for producing an engine operating signal when the engine speed signal exceeds idling speed; a terminal for grounding a circuit and for producing a grounding signal during the grounding; first gate means responsive to said engine operating signal of said second comparator and to the grounding signal for producing a first signal having a first logic level during the presence of the grounding signal and a second signal having a different, second logic level during the absence of the grounding signal and during the presence of the engine operating signal; second means responsive to the second signal having the second logic level for producing a third signal; second gate means for providing a fourth signal upon occurrence of said failure output of said starter operation diagnosing circuit means and the first signal having the first logic level and respectively said second signal; and warning means operated by said fourth signal from said second gate means.