GM Service Manual Online
For 1990-2009 cars only

Inside Rearview Mirror with the Automatic Day-Night Feature System Components

The inside rearview mirror with the automatic day-night feature system consists of the following components:

    • Inside rearview mirror
    • Driver outside mirror with the automatic day-night feature

Inside Rearview Mirror with the Automatic Day-Night Feature Switches

The inside rearview mirror has 5 switches that perform the following functions:

    • The HomeLink transmitter switches
    • The automatic day-night mirror switch
    • The map light switch

Power and Ground of the Inside Rearview Mirror

    • With the ignition ON, ignition voltage is supplied to the mirror from the IGN E fuse in the underhood fuse block.
    • Ground for the mirror is provided by G301.

Inside Rearview Mirror with the Automatic Day-Night Feature System Operation

The inside rearview mirror uses 2 photocell sensors. One sensor is the headlight sensor, located on the rear side of the mirror. The other sensor is the ambient light sensor, located on the front of the mirror or windshield side. With the automatic day-night feature enabled, the mirror uses the ambient light sensor to determine the exterior light condition. With a low light condition detected, and a high light condition from behind at the headlight sensor, the inside rearview mirror will automatically darken the face of the mirror.

In the daytime, the mirror is in a normal state because of the high light condition that is indicated by the ambient light sensor. With the gear selector lever in the REVERSE position, backup lamp supply voltage is supplied as an input to the inside rearview mirror. In night time conditions only, the mirror monitors this input to disable the automatic day-night feature which allows the face to gradually change to a normal state. This allows the driver to clearly see objects in the mirror when backing up. The mirror also disables the automatic day-night feature when when either door is opened and the courtesy lights are illuminated.

Driver Outside Rearview Mirror with the Automatic Day-Night Feature Operation

The drivers outside rearview mirror will also darken when the inside rearview mirror darkens. The inside rearview mirror supplies a low reference circuit and a control circuit to the drivers outside rearview mirror.