Thursday, 30 June 2005 17:00

Head-Up Display units making comeback

Written by I-CAR Advantage Online
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What's a HUD? Head-Up Display (HUD) units project information from the instrument panel to the front of the windshield so the driver can maintain focus on the road. The projected image usually appears to hover over the hood of the vehicle, a distance close to where the driver is already focused. This might be why this accessory is offered not only as a "high-tech" gadget, but also a safety feature. 

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Figure 1. A Siemens VDO multi-color Head-Up Display is available on BMW 5 and 6 Series vehicles. (Courtesy of Siemens VDO)
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Figure 2. The "Mode" and "Page" buttons on the 2005 Chevrolet Corvette convertible give the driver control of what information is displayed on the HUD.
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Figure 3. Glass located on top of the instrument panel is one indication that a vehicle is equipped with an HUD.

Adapted from military aircraft technology, HUD units were first introduced to the automotive industry in the late 1980s. Examples of the first vehicles to offer this feature include the 1988 Oldsmobile Cutlass Supreme and the Pontiac Grand Prix. Because of limited daytime visibility, bulkiness, and the high amount of energy required to power the units, popularity quickly faded with early models. Advancements in technology and public demand for safety features may be why HUD is making a comeback. New illumination processes consume less energy and produce brighter images that remain visible in direct sunlight.

Today's HUD

Today's HUD will typically use a bright LED-backlit liquid crystal display along with a series of mirrors to direct the image to the windshield. LEDs are more efficient and produce much less heat than the fluorescent and incandescent light sources used in early HUD modules. Both single-colored monochrome and multi- colored displays are available. Multiple colors offer the ability to highlight certain warnings or safety features. For example, speed and blinker activity may be displayed in green, and red may be reserved for warnings such as low tire pressure or low fuel. BMW uses a red and green LED array. Orange is used for general information and red, yellow, and green are used for prioritized messaging (see Figure 1).

Newer HUD units may have the ability to automatically adjust the brightness of the display to conform to ambient light conditions. In direct sunlight, the brightness is intensified to remain visible. The display gets dimmer in dark conditions so the image does not become a distraction for the driver. HUD units typically provide controls to turn the display on or off, manually adjust the brightness, and position the image. Some systems, like on the 2005 Chevrolet Corvette, give the driver even more control with the ability to choose which information is displayed on the windshield (see Figure 2).

Other features can be integrated into the HUD as well. Some vehicles, like the BMW 5 Series, use the HUD to supplement the navigation system. The 2005 Cadillac Deville uses the HUD for the Night Vision option.

Safety feature or distraction?

Many are skeptical about whether a HUD has the ability to prevent accidents or potentially cause them. The fact remains that an image is in front of the windshield, and that can be considered a distraction. Often, people with this skepticism find that after actually driving a vehicle equipped with HUD, it is not a distraction at all and very helpful.

A study at the University of Illinois at Champaign-Urbana concluded that HUD can effectively keep a driver's eyes on the road and therefore more alert to unexpected traffic events. However, if the image is located too close to the driver's line of sight, it may impair the driver's ability to comprehend sudden hazards. The study concluded that a more appropriate location would be lower on the windshield and not in direct alignment with the driver's view of the road ahead.

Repair considerations

In regards to repair, it is important to know if a vehicle is equipped with HUD. A glass surface on top of the instrument panel or labeled switches and controls may be indications (see Figure 3). The windshield is part of the HUD system. A special type of windshield is required to properly display the HUD image.

Normal windshields may reflect distorted or double images. Special windshields are manufactured with a wedge-shaped polymer layer sandwiched between two pieces of glass. The angle of the wedge is very small, measured in milliradians (one milliradian is 0.57), and is specific for each vehicle. Some vehicles may come with a HUD as standard equipment, but most likely it is offered as an optional accessory. It will be necessary to specify that the vehicle has the HUD option when ordering a replacement windshield.

The HUD modules are normally located inside the instrument panel and should be protected against most minor collisions. If the HUD is not working, a DVOM and symptom flowchart may be used to determine the problem. Troubleshooting may lead to a blown fuse, bad switch, or damaged wiring. Inner parts of HUD modules are not repairable and require complete module replacement if it is determined that the module is non-functional.

Removing HUD modules will likely involve removing the upper trim pad on the instrument panel, unbolting the securing fasteners, and disconnecting electrical connectors. When reinstalling parts, make sure that all of the correct parts are ordered and follow vehicle maker torque specifications for fasteners. Sealant or thread locking compounds may affect the torque and joint clamping force of fasteners. Do not use these unless specified by service procedure instructions.

After the installation is completed, make sure the system is functioning properly. Verify that the digital readings on the HUD correspond to the readings on the instrument panel. If a difference is determined, refer to the vehicle service information for allowable plus/minus accuracy specifications and repair procedures. A scan tool may be required to determine what part displays the greatest error.


Today's HUD units are more ad-vanced and efficient than their predecessors. They are ideal for displaying the many new features in which drivers would normally have to look down to the instrument panel for. Because of this, they may become a popular accessory and installed in more vehicles in the future. It is important for technicians to know if a vehicle is equipped with such a device and have a basic understanding of how they work. The windshield is a vital part of a HUD system, and proper replacement is important for the system to function effectively.

This Advantage Online article first appeared in the I-CAR e-newsletter, which is published and distributed free of charge. I-CAR, the Inter-Industry Conference on Auto Collision Repair, is a not-for-profit international training organization that researches and develops quality technical education programs related to collision repair. To learn more about I-CAR, and to subscribe to the free e-newsletter, visit or contact I-CAR Marketing Communications Specialist Brandon Eckenrode at Brandon.Eckenrode


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