GM Service Manual Online
For 1990-2009 cars only

The inside rearview mirror (electrochromic) uses 2 photocell sensors to determine light conditions in the front and the back of the vehicle. Turning the mirror to the OFF position causes the mirror to be in a clear state.

The mirror receives its voltage from the Sunroof fuse in the fuse block through circuit 343. Ground is supplied through circuit 350 from G302. Turn the switch to the ON position will cause the backlight of the switch turns on. In the daytime, the mirror remains in a clear state. At night, the mirror remains in a clear state until the glare of headlamps from behind increases to a point that exceeds the preset sensitivity of the mirror. The mirror then becomes darker to absorb the glare. It will remain dark until the glare of the headlamps diminish and then returns to a clear state.

A voltage is fed from the B/U LP fuse in the underhood accessory wiring junction block through circuit 840 to the transaxle range switch. When the gear select lever is in the reverse position, voltage is sent through circuit 24 to the mirror. If the mirror is in the darkened state, this input causes the mirror to change to a clear state regardless of any glare. Taking the gear select lever out of reverse causes the mirror to return to normal operation.