There is provided a heat flux sensor with first and second interlayer connection members composed of different metals from each other of which metal atoms maintain a predetermined crystal structure embedded in first and second via holes of a thermoplastic resin made insulating substrate, the first and the second interlayer connection members are connected in series alternately, and a control unit that performs abnormality determination of a heating element disposed in a vehicle. The heat flux sensor is provided to the heating element and outputs a sensor signal corresponding to heat flux between the heating element and an outside air, and the control unit determines based on the sensor signal that there is abnormality in the heating element when the heat flux between the heating element and the outside air is out of a predetermined range.