BATTERY HEATER FAILURE DIAGNOSTIC DEVICE FOR VEHICLE

To provide a battery heater failure diagnostic device for a vehicle capable of diagnosing failure of a battery heater with a high degree of accuracy, a battery output sensor capable of detecting a battery output value that is a current value or a voltage value of a battery is provided. When a specified failure diagnosis condition is satisfied, a first control for stopping actuation of a battery heater and at least one non-heater device and a second control for actuating the battery heater while maintaining a stop of the actuation of the at least one non-heater device after execution of the first control are executed. The failure of the battery heater is diagnosed based on battery output values detected by the battery output sensor during execution of the first control and during execution of the second control.