The wireless access module has an automatic location function that automatically recognizes the position of the tire air pressure sensor while the vehicle is running. The wireless access module identifies the position of each tire air pressure sensor based on the wheel speed information from the EHCU. When the vehicle speed is 30 km/h {19 mph} or more and the accumulated driving time of a maximum of 10 minutes has passed, the automatic location is complete. If the wireless access module detects that the automatic location is not complete within the specified time, the DTC is set.