Diagnosis apparatus for diagnosing variable valve timing mechanism

摘要

Faults in a variable valve timing mechanism can be accurately diagnosed without influence of a detection error by a crank angle sensor and the like. A phase difference of a crank angle between a standard angular signal REF output from the crank angle sensor and a phase detection signal detected at a predetermined angular position of a cam shaft is counted every control state of the variable valve timing mechanism. Next, a variation between a phase difference counted at a time of OFF control state and a phase difference counted at a time of ON control state is calculated as a diagnosis parameter. Then, in the case that the diagnosis parameter is smaller than a standard value for determination, a fault in the variable valve timing mechanism is determined.