Circuit Description
WARNING: This page is about a different car, the 1998 Cadillac Seville. However, it is still accessible from the selected car via links, so may be relevant.
The Instrument Panel Integration Module (IPM) receives an input from the ambient light sensor. IPM supplies ground for the sensor through the sensor return circuit. Sensor resistance is 23,000 ohms for bright light and 31,000 ohms or greater for complete darkness. As resistance varies, voltage input to IPM changes.
IPM determines whether it is light or dark outside, then sends a message via the Class-II serial data line to the Dash Integration Module (DIM) and the Rear Integration Module (RIM).
IPM will set DTC anytime it detects that ambient sensor input voltage is out of range.