Electronic control unit and method measuring and using electric power-off period

摘要

In an ECU for vehicles, a clock IC operates with sub power and measures time continuously irrespective of whether a microcomputer is operating. The microcomputer determines whether the clock IC has been reset on the basis of a history indicating that the sub power has fallen below a data holding voltage of an SRAM which also operates on the sub power. Alternatively, the microcomputer determines whether the clock IC has been reset by checking data held in the SRAM. The microcomputer determines failure of a water temperature sensor from a soak time calculated from time data from the clock IC and a detection value of the water temperature sensor on restarting of the engine. When the clock IC has been reset, the microcomputer prohibits this failure determination of the water temperature sensor.