The purpose of the System Voltage is to detect an excessively low or high system voltage that may be caused by a malfunctioning charging system.

System Voltage is the ignition voltage potential at the Powertrain Control Module (ECM/PCM)ECM/PCM measures and compares voltage from ignition key and each relay. With this mechanism, ECM/PCM knows if the main relay switch turns on after IG on or if turns OFF after IG off.