An electronic control unit includes a control portion and a soak timer. The control portion acquires first time information of a clock device when a power switch is turned off and stores the first time information in a nonvolatile storage portion. The control portion acquires second time information of the clock device when the soak timer activates the control portion or when the control portion receives an activation request. The control portion calculates a first time difference between the second time information and the first time information stored in the nonvolatile storage portion and determines an abnormality of the soak timer based a difference between the first time difference and the soak timer value of the soak timer.