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)

ECM measures and compares voltage from ignition key and each relay. With this mechanism, ECM knows if the main relay switch turns on after IG on or if turns OFF after IG off.

Main relay is located in EMS box of junction box.