2004 GMC Envoy Headlamp Alignment Adjust Cost

A vehicle's headlamps (or headlights) serve to illuminate the road during nighttime driving and to make the vehicle more visible during daytime driving. The headlamp system includes a low beam used for normal driving, and a high beam that is only to be used when no other cars are present on the road. While cars of the past relied on round, sealed-beam lamps, modern vehicles feature headlamps with aerodynamic shapes and replaceable halogen bulbs. Some headlamps are powered with high intensity discharge (HID) bulbs that put out more light. These lamps are also known as "Xenon headlamps" and stand out by their bright bluish-white glow. Most headlamps need to be manually aimed or adjusted so that they focus at the correct point on the road ahead of the vehicle.

A headlamp incorporates a bulb placed in front of a reflector (or a series of mirrors) that projects a beam of light through a lens and directs the beam to the road ahead. Halogen lamps produce more light with less heat output than older incandescent bulbs due to the halogen gas injected into the bulb. HID, or “Xenon,” headlamps provide even more light by producing an electrical arc for illumination rather than a glowing tungsten filament. Headlamp adjustment involves a technician manually aiming the headlamps so that they focus in the correct area ahead of the vehicle. Some late model vehicles feature self-leveling headlamps that that remain level with the road regardless of the angle of the vehicle. Vehicles with "adaptive headlamps" use a motor to shift the focus of the lamp to follow curves in the road.

Symptoms of improperly or mis-aligned headlamps include poor visibility at night, blank spots on the ground ahead of the vehicle, or headlamps that light up the sides of the road or surrounding landscape (i.e. trees, sidewalks). If oncoming drivers tend to flash their high beams, the problem could be due to improperly aligned lamps pointing toward the oncoming traffic instead of toward the road ahead.