A-3: ECM Power & Ground Circuit Check: Condition
WARNING: This page is about a different car, the 2002 Suzuki Grand Vitara. However, it is still accessible from the selected car via links, so may be relevant.
When ignition switch is turned to ON position, main relay is energized by the Engine Control Module (ECM)/Powertrain Control Module (PCM) and supplies ECM (PCM) with main power. As ECM (PCM) is supplied with main power, it will turn ON the MIL. After engine starts, MIL will turn OFF if no malfunction is detected. If a malfunction is detected, MIL will remain ON until system is repaired.