Electronic control unit and method for measuring engine soak time

摘要

In an ECU for vehicles, a microcomputer operates with a main power from a battery, and a clock IC operates with sub power from the battery and measures time continuously irrespective of whether the microcomputer is operating. The microcomputer stores time data of the clock IC just before the supply of main power is turned off, and calculates a soak time or engine stop period from the stored time data and a current time data of the clock IC only after the supply of main power is turned on again and engine cranking is completed. This soak time represents the engine stop period. Operation of a cooling water temperature sensor or the like is checked by using the sensor output in relation to the calculated soak time.