While your Chevy's lighting system is pretty simple to fix, a few things can go wrong, which can make diagnosis a little more difficult than anticipated. Still, headlight problems are no problem with the right information. Whether your Chevy TrailBlazer lights aren't working, or your Chevy Corvette, the following diagnostic process will help you figure out why your Chevy's headlights aren't working.
What’s Going On With Your Headlights
First, you’ll need to pinpoint the problem, so here are some common headlight trouble scenarios.
Only one headlight works: If only one of your Chevy’s headlights is working, the other headlight likely has a burnt out bulb. You can do a visual inspection of the build to determine if it has gone bad. A burnt out bulb is usually discolored and pieces of the filament will be loose inside the bulb.
If a visual inspection shows the bulb is still good, there may also be a broken wire in the harness to that light. A wiring issue will require a check of wires with a multimeter with the help of your vehicle’s schematics.
Only the low-beams or high-beams work: If your headlights both work but only when the low-beams or high-beams are on, the problem is likely with the dimmer switch. Modern cars have this switch on the steering column or dashboard, while older cars usually have a dimmer switch on the floorboard.
This switch also controls the turning signals. Replacing it requires removing part of the steering column or dash, depending on the year/model.
Neither side works: If both headlights are dead, it’s probably not a problem with the bulbs, but it’s worth a check. The most likely scenario is that the fuse is bad. Remove the fuse for the headlights and check it. When a fuse is bad, it’s obvious because the filament will have a gap in it. You can also check it with a multimeter.
If the fuse is fine, check the headlight relay or control module. If the system uses a relay, pull it and shake it to listen for rattles — if it does, replace the relay. To check the module, you’ll need to find it first, which may be very difficult and require a service manual to hunt it down. Once you locate it, it can be tested with a multimeter.
Headlights dim when you rev your vehicle’s engine: This is usually caused by a charging system problem. Check the voltage of your alternator while the engine is idling and consult your repair manual for specifications.
Headlights work, but not very well: If your headlights don’t provide enough light for the road ahead, it can come from several problems. Fogging of the lenses, clouding inside the housing, moisture inside the housing, and headlights that are not aimed properly are the most common causes.
Remove the lenses to clean or replace when fogginess or clouding occurs. To remove moisture, drill a small hole in the bottom half of the lens to allow water to escape and dry out.
To check alignment, park about 10 feet from the garage door wall and turn the lights on. Low beams should be aimed straight forward and hit no higher than your hood line. The high beams should move slightly, but not too much higher than the low beams.
If they need to be adjusted, there are screws on the back or top of the housing to allow you to do so. At this point, you will probably need to refer to service literature on making adjustments for your specific year/model.