Micro control units (MCU) used for embedded systems are often required to function under strong electrical noise. In this paper, we analyze the effects of such electrical noise by FMEA (Failure Mode and Effect Analysis). We revise FMEA by adding columns which show the context of the fault and time after the fault. By our method, we can enumerate faults of complex systems like MCU from their components whose fault modes are easier to enumerate. We demonstrate that the effects of electrical noise to MCU can be summarized by only few faults.