A3: Engine Control Module Power & Ground Circuit Check/Engine Does Not Start: Condition
WARNING: This page is about a different car, the 2002 Suzuki Esteem. However, it is still accessible from the selected car via links, so may be relevant.
When ignition is turned on, main relay is energized by the Engine Control Module (ECM) and supplies ECM with main power. As ECM is supplied with main power, it will illuminate MIL. After engine starts, MIL will turn off if no malfunction is detected. If a malfunction is detected, MIL will remain illuminated until system is repaired.