afs is functioning in the normal area is determined using the method described by reference to fig3 s 109 when the afs remains normal ok the induction air volume calculated based on the pressure sensor output pb is stored in the memory as a parameter indicating the driving area in the current monitoring s 111 a current value of an ok timer is stored in the memory and a ng timer is held then advancing to step s 115 in step s 115 whether or not there is a log of past failures is determined and if there is then advance to step s 117 where whether or not the current driving area stored in s 111 overlaps the driving area of the log of past failures is determined when it is determined that the two areas overlap the normality determination of the afs is permitted s 119 whereas when they do not the normality determination of the afs is not permitted s 121 when a failure of the afs is determined in the past and there exists a log of failure only in the event that the aft is in the normal area at a driving area equivalent to the driving area resulting when the failure determination is made in the past the normality determination is permitted this is because in case the driving areas are different there may exist a possibility that determinations become different next in step s 123 whether or not an output value from the afs.