Diagnostic system for variable valve timing control system

摘要

A diagnostic system makes a diagnosis on a variable valve timing control system mounted on an internal combustion engine by forcibly switching the valve timing control system from an operative state to an in operative state. The diagnostic system comprises sensors for detecting a variation of an operating state of an internal combustion engine, based on the forcible switching operation, and for detecting a throttle valve opening of the engine. The diagnostic system makes the diagnosis by comparing a variation of rate of flow of intake-air with a predetermined reference value to determine whether the valve timing control system operates normally or abnormally. The diagnostic system provides both a predetermined diagnostic preparatory period and a predetermined actual diagnostic period. The diagnostic system calculates a variation of the throttle valve opening, varied from the throttle valve opening detected at the beginning of the predetermined diagnostic preparatory period before the forcible switching operation, and inhibits the diagnosis of the valve timing control system when the variation of the throttle valve opening exceeds a predetermined threshold.