The No. 2 main body ECU receives the half-latch switch, pawl switch and lower tail gate courtesy switch signals from the lower tail gate lock assembly LH and detects the open/closed status of the lower tail gate. DTC B225D is stored when the No. 2 main body ECU receives a half-latch switch, pawl switch or lower tail gate courtesy switch malfunction signal from the lower tail gate lock assembly LH.