Lost low beam headlight



The low beam on my Buick will occasionally go out. I’m left with only my high beam. The next time I drive it, my low beams come back on. Mechanic can’t find the cause. any suggestions where to look for cause?


These intermittent problems are always tough to diagnose. Sometimes I feel like the best thing to do is just cope until it finishes breaking. Then it’s easier to figure out what’s wrong. That said, …

SOMETIMES light bulb filaments go intermittent. If you had only one side going out, I’d suggest replacng the bulb just because it’s easy (maybe) and cheap. (Many experts here suggest replacing both bulbs when you have to do one. Some kind of “the other one must be ready to fail, too” theory", but I don’t hold by that.)

However, I think you are saying that both go out, so we have to look for something common to both sides. I assume you have tried switching the headlights off/on, so (maybe) the problem is not in the switch. Most cars have a relay that switches the headlights. Try replacing that (also easy and cheap). If not that, then we have to suspect the electrical connections.

Does the car have any day/night sensor for turning on/ff running lights? Do you know if the headlight switch controls the circuit (i.e., the relay) directly, or is it going through a computer?

Soem questions to tickle our thinking – When you say the low beam goes out, and then next time you drive it they come back on. Does the low beam come on every time you switch off the car and restart? Do the low’s come on if you restart right away (that is a handy temporary work-around), or does the car have to sit for a while? Do the low’s ever come back on without the car’s being switched off and restarted? Will the low’s come on if, without turning off the car, you just turn off the headlights and then turn them back on?


I have replaced both headlights. This car does have the sensor but I don’t know if the headlight switch controls the circuit or if it goes thru the computer. Possibly my mechanic can answer that question for me. When the low beams goes out, if I turn the car off and then back on again, the beam does not come on. However, once it has sat idle for a time (i.e. overnight) it always comes back on the next time I start the car. The low beam will not come back on if I turn them on and off manually. The beam never comes back on when they have just gone out on me…only coming on the next day when I drive the car again. Thanks for your comments and I await any further information/suggestions you can provide.


Well, them’s all the wrong answers, but that that’s what I expected. Almost too many things to guess at, especially if the computer gets involved. The fact that the car has to sit for a while hints at something having to cool off, but hard to guess what might heat up intermittently.

Try changing the relay (but I have a feeling you have already done that). Yeah, I’m just guessing and throwing parts at it, but the parts are cheap and the next rational step is hard.

If that does not help, then unless you get lucky and it fails when you have time to test it, maybe just unplug and re-plug all the connectors in the headlight chain. That would include the sensor and the computer. You’ll need a manual to identify them all. An alternative procedure would be to turn on the low’s and wiggle connectors and cable harnesses to see if you can find one intermittent. That is, if wigging makes the lights go off, you have found the culprit.

As I said, sometimes it’s best to wait for it to finish breaking.