How to Adjust Semi Truck Headlights for DOT Compliance: Complete Guide

Semi Truck Headlight Adjustment for DOT Compliance

Misaimed headlights are one of the most overlooked safety issues on commercial trucks. Too high and you blind oncoming traffic. Too low and you can't see road hazards. The DOT requires headlights to be aimed within specific parameters — and improperly aimed headlights are a common inspection failure.

When Should You Adjust Headlights?

• After replacing headlight assemblies
• After any front-end collision or fender-bender
• When other drivers flash their high beams at you
• If you notice reduced visibility at night
• During annual DOT inspection preparation
• After changing suspension components

What You'll Need

• Flat, level surface (parking lot)
• Wall or garage door (light-colored preferred)
• Measuring tape (25 ft minimum)
• Masking tape
• Phillips or Torx screwdriver (varies by truck)
• Headlight aim tool (optional but recommended)

The 25-Foot Wall Method

Step 1: Prepare the Truck

Park the truck on a level surface, 25 feet from a flat wall. The truck should be at normal operating weight — if you're usually loaded, do the adjustment loaded. Tires should be at proper inflation pressure. Turn on the low beams.

Step 2: Mark the Reference Points

On the wall, mark the center of each headlight beam with masking tape. Also mark the truck centerline. These marks represent where the beams are currently hitting.

Step 3: Vertical Adjustment

The low beam cutoff line should be at or slightly below (no more than 2 inches) the center of the headlight at 25 feet. Use the vertical adjustment screw on the back of the headlight assembly to move the beam up or down.

Step 4: Horizontal Adjustment

Each beam should be aimed straight ahead or very slightly to the right (passenger side). The hot spot should not cross the truck's centerline. Use the horizontal adjustment screw to correct any lateral misalignment.

Adjustment Screw Locations by Brand

DOT Requirements (FMVSS 108)

Federal Motor Vehicle Safety Standard 108 requires that headlights meet specific photometric requirements. For commercial motor vehicles in roadside inspections, officers check that headlights are properly aimed using either a headlight aiming device or the wall test method. Out-of-adjustment headlights can result in a vehicle being placed out of service.

LED vs Halogen Adjustment Differences

LED headlights typically have a sharper beam cutoff than halogen, making precise adjustment even more important. The good news is that sharp cutoff makes it easier to see exactly where the beam is aimed against a wall. If you've recently upgraded to LED headlights, always re-aim them — the beam pattern is likely different from the original halogen units.

Professional Headlight Aiming

For the most precise results, many truck shops use a photometric headlight aimer. These devices attach to the front of the headlight and measure the exact beam angle. If your fleet has 10+ trucks, investing in a headlight aimer tool pays for itself quickly.

Upgrade your headlights: Browse DOT-compliant headlights for all major truck brands at EverTrust — every assembly is pre-aimed for easy installation.