Circuit Description
WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
There should always be a steady malfunction indicator lamp (MIL) when the ignition switch is in the ON position and the engine is not running. System voltage is applied to the indicator bulb and the instrument panel cluster (IPC) provides a path to ground. Once the engine starts, the IPC turns OFF the MIL. When an engine control system malfunction occurs, the powertrain control module (PCM) sends a message over the controller area network (CAN) to the body control module (BCM) requesting the MIL. The BCM then sends a message to the IPC over class 2 requesting MIL illumination.