High beam not working on Silverado truck

For a few weeks I am borrowing a Chevy Silverado truck whose high beam lights are not working and I’d like to take a try at fixing it. In old cars you could just follow wires and know where the problem was but I have no idea how things might work now with all those computers and stuff. Is this something I can take a stab at or am I better off taking it to a shop (or just returning the truck as it is)?

The blue indicator on the panel lights up but none of the headlights do. This leads me to believe it is not that the filaments are all out but rather that the cause lies elsewhere.

I would check the bulbs first. An ohmeter can check the high beam circuit of the bulb very easily.

I was late on the edit, but did you ask the owner if they worked before? Hopefully he is an honest guy that would tell you if they weren’t.

I don’t know what your logic is here, but I’d say it’s flawed. If the indicator lights up, then almost certainly the high beam circuits are energized. And if the circuits are energized but the bulbs don’t light up, it’s a 99% probability that the bulbs are faulty.

Test for power at the headlight connectors (make you’re checking the high-beam wires, not the low-beam ones) or replace the bulbs. If there’s no power, or the bulbs still don’t light, then start thinking about a different cause. If it gets to that and you want help, provide the year, model (there is a Silverado model in some years, but in others it’s a trim level, not a model - if it’s a C1500 2WD pickup, that’s what we’d need to know), and engine size (liters, not number of cylinders). With that info, I can find the correct wiring diagram and give more accurate advice.

I believe on most cars, the failure of one filament will result in both bulbs not lighting up, so most likely you just need one(1) new bulb.

I have never seen or heard of that. It’s certainly not true of most cars, and I question whether it’s true of any.

I see, I am wrong about it being most cars, then. It was like that on my old Mercedes.

If you have to replace the headlight bulbs it’s not terribly expensive - I did my 1998 F150 last month, the middle-of-the-line Sylvania bulbs were about $25-30 each and they had a slightly cheaper set as well ($20? each). Hopefully the Silverado makes it easier to replace them than on the Ford - the driver’s side bulb on the F150 is a real hassle to get at, I had to move some things around and still got my knuckles barked pretty good.

So your logic says it is more probable that four separate filaments failed all at once than a single wire or control signal? I guess we have different logic then because my logic tells me that it is more probable that one thing failed rather than four.

I do not know the exact model and I even don’t know how to find out. It is a 2007 and I saw something under the hood saying “4800”, which I take to be the engine size (4800 cc?) and the owner could only tell me she thought it was a 1500 (whatever that means and she’s not even sure about that). I’ll try to find out more.

It certainly would be helpful to have the wiring diagram or at least to know how the lights are powered.

The parts you’re thinking have failed tend not to fail so soon, and if its a 2007 model, then non-bulb issues will be covered under warranty. I’ve owned close to 20 vehicles in my life, and the only time I’ve had a headlight problem that wasn’t related to the bulbs going out was when the vehicle was pushing its second decade of life.

The light dawns. We both have reasonable logic, but are working with different assumptions. Apparently you assumed that the low beam lamps are combination low/high beams, and thus with the addition of the high-beam-only lamps there would be four lamps on high beam (this is the way all cars did it for years). I assumed that the low beam lamps were low-beam-only, thus giving only two lamps on high beam (this has become increasingly popular over the last several years). I’ll check a wiring diagram and see which assumption was correct.

He probably only needs to know that it’s a 2007 Silverado 1500 - that would make Silverado the model, not the trim package. Do you know if it’s an LT, WT or LTZ? There should be a badge on the back.

1500 = 1.5 ton, incidentally.

If the regular beams work, that’s two filaments, not four. Headlight problems are almost always bulb-related rather than wiring or other electrical problems.

Ah, you might want to follow Gary T’s advice. According to this website, a 2007 Silverado uses a 2006* low beam, and a 2005* high beam bulb. The reason I mention this is that a 2006* bulb is a single filament so it does not have a second filament that gets brighter when the high beams are on. So at this point you are looking at a failure of two filaments, not four. Also some vehicles turn off the low beams when the high beams turn on. So it is possible that when you hit the highs, all four lights could go out.

Look, I understand that the race doesn’t always go to the swift or the strong, but that is the way to bet.
The two most likely points of failure for this vehicle are the bulbs, or a fuse, unless some very substandard body work has been done. It is also possible that the step relay (what actually switches the high beams on) could be bad, but I would rate the chance of this on an 07 vehicle as being very slim.
Check the light bulbs first. Then the fuse, then and only then worry about anything else.

  • These are part numbers, not years

Really Not All That Bright and Rick beat me to it, but yes - on this model, two lamps are low-beam-only, the other two are high-beam-only.

The headlight/daytime running light circuits use two switches, three relays, and the body control module (BCM) to operate various parts of the system. The function of the high-beam indicator proves that the switches are working. The failure could be in the BCM, the high-beam relay, or the bulbs*. Having the two high-beam bulbs burnt out is not terribly uncommon. If there is not power to the bulbs, the relay (in the underhood fuse box) is the next thing to test. After that the BCM is the remaining prime suspect, but I wouldn’t replace it until a thorough test of its relevant inputs and outputs has been done.

*Poor connections and faulty wires are also possibilities, but are fortunately rare.

Please tell me that you have some data available at home, and you aren’t still at the shop this late.

I was not aware of this practice. I’ll have a look tomorrow and see what I can find.

Yes, I can access Alldata from home. Actually left the shop a bit earlier than usual today.

This made me chuckle.:slight_smile: It must be an automotive thing. I have access to both Chryslers repair and parts catalogs from home.

I need to get a hobby.

OK, the truck model is LT so I guess that makes it something like Chevy Silverado LT 1500 4800. The manual lists dozens of models depending on multitude of factors like drivetrain etc. How could I find out exactly which model it is?

I checked the lightbulbs and, indeed they are all single filament. The one I checked appeared under a magnifying glass to have an intact filament. I could not exchange it with the low beam to test it because the connector is slightly different. The marks on it are Philips HB3 9005 22S 12V 60W

I guess the question would be if these lights are both controlled by some relay or fuse which I might check.

Filaments can be broken and still look intact.