Many control units have applied to vehicle as it becomes more eletrolnical. These units control their own system based on information from diverse sensors. Therefore necessity of common use of diverse sensor information and importance of stable power supply are gathering strength. Battery sensor is mounted on battery (-) terminal. It transmits battery voltage, current, temperature information to ECM. ECM controls generating voltage by duty cycle based on these signals.

ECM sets this code when there is difference between battery voltage at power supply terminal of ECM and the voltage from battery senor.