Failure detecting device for a power supply changeover switch

摘要

A battery and an electrically heated catalytic converter (EHC) are connected to an alternator in a parallel arrangement via a changeover switch. The changeover switch operates between a first position where it connects the battery to the alternator and a second position where it connects the EHC to the alternator. An electronic control unit (ECU) is provided for controlling the changeover switch and the alternator. When the changeover switch is to be switched between the first and the second position, the ECU first terminates the power generation of the alternator before it actually switches the changeover switch in order to reduce the electric current flowing through the switch. In the switching operation of the changeover switch from the first position to the second position, the ECU determines that sticking of the changeover switch at the first position occurs if the output voltage of the alternator does not become lower than a predetermined value when a predetermined time has lapsed after the switching operation started.