Switch or Bulbs to Blame for Low-Beam Outages?

Dear Car Talk

Dear Car Talk | Sep 07, 2017

Dear Car Talk:

My wife has a 2007 Solara. This is her second one. I have had the same problem with both of them. Frequently, one -- sometimes the left, other times the right and occasionally both -- of the low beams will go out. If I just move the headlight switch from Auto to either Off or On and then back to the Auto position, the problem is fixed for a while. I've taken the car to the dealer, and they can find nothing wrong. I've replaced the bulbs, and so did the dealer. But nothing has fixed the problem. Do you have any ideas? -- Ken

There are two possibilities, Ken. If your Solara has HID (high-intensity discharge, sometimes called Xenon) headlights, it could very well be bad bulbs. Priuses, Camrys and Solaras had lots of problems with their HID bulbs failing prematurely.

Unlike halogen bulbs, HID bulbs can fail intermittently -- like you describe. So your bulbs may just be failing sooner than they're supposed to. If your dealer didn't mention that, it's either because he doesn't have an answer except "more bulbs," or because you have standard halogen bulbs.

If you do have halogen bulbs, then I'd guess that you have a bad multifunction switch, since fiddling with the switch always seems to fix it. That's the stalk that comes out of the left side of the steering column and operates the turn signals and headlights.

If both of your headlights were always failing simultaneously, I might suspect the daylight sensor, which makes the lights go on and off when you set the switch to Automatic. But since that sensor merely turns the switch on and off, it would affect both headlights, not just the right or left.

If you have halogen bulbs, I doubt it's the bulbs themselves. Standard bulbs pretty much either work, or they don't. So if you can get a bulb that's dead to come back to life and then stay on by monkeying with the switch, the bulb is unlikely to be the problem.

The multifunction switch could fail intermittently, like you describe. If it happens to be working fine the day you take it to the dealership, they would find nothing wrong.

Under the mechanics' code of conduct, they still shouldn't have let you leave without selling you a new multifunction switch and a new transmission, but that's water under the bridge now.

Of course, the best thing to do would be to get your car to the shop when the lights are misbehaving. Then a mechanic can check and see if there's current reaching the bulb sockets. If there's no current getting to the bulbs, then you'd strongly suspect the switch.

But as we know, headlights usually fail when? At night! When the dealership is closed. So you may have to take your best guess. You can't just drive around at night with your lights going out.

So ask the parts department how often they have to replace multifunction switches on Toyotas in their shop. If their answer is anything other than "never," ask them to try one for you, Ken.

And if it doesn't fix the problem, maybe they'll be nice enough to take the part back and charge you just for the labor. Then you can buy one of those 250-watt halogen work lights at Home Depot, plug it into the cigarette lighter and prop it up on your dashboard. Good luck, Ken.

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