Malfunction Indicator Lamp (MIL)
WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
The MIL is illuminated when a diagnostic trouble code (DTC) is detected by the PCM. The instrument cluster receives the MIL data from the PCM over the communication network.