2005 GMC Envoy Owner's Manual - Page 152

Automatic Headlamp System When it is dark enough outside, your Automatic Headlamp System will turn on your headlamps at the normal brightness along with other lamps such as the taillamps, sidemarker, parking lamps and the instrument panel lights. The radio lights will also be on. Your vehicle is equipped with a light sensor on the top of the instrument panel. Be sure it is not covered or the system will be on whenever the ignition is on. The system may also turn on your lights when driving through a parking garage, heavy overcast weather or a tunnel. This is normal. There is a delay in the transition between the daytime and nighttime operation of the Daytime Running Lamps (DRL) and the automatic headlamp systems, so that driving under bridges or bright overhead street lights does not affect the system. The DRL and automatic headlamp system will only be affected when the light sensor sees a change in lighting lasting longer than the delay. If you start your vehicle in a dark garage, the automatic headlamp system will come on immediately. Once you leave the garage, it will take about one minute for the automatic headlamp system to change to DRL if it is light outside. During that delay, your instrument panel cluster may not be as bright as usual. Make sure your instrument panel brightness control is in the full bright position. To idle your vehicle with the automatic headlamp system off, set the parking brake while the ignition is off. Then start your vehicle. The automatic headlamp system will stay off until you release the parking brake, shift out of park or turn the exterior lamp control to the off position as described in "Exterior Lamps" listed previously. 3-16