Dear Tom and Ray:
I have a 2000 Chevrolet Astro Van. The emergency warning device (aka, the horn) will work only if the outside temperature is above 55 degrees F. Seriously — I'm not making this up. Sometimes, if the temperature is near 55 degrees, and if I hold the horn button down for between one and three minutes, the horn will work. Once I get the horn to blow, it will work all day from then on. I'm about to buy an add-on button and attach it to an aftermarket horn, maybe with the "Dukes of Hazzard" theme. All kidding aside, it is a serious problem because I live in a cold part of the country, and for many months, the days above 55 are few and far between. Please help. Thank you! — Dan
Ray: No, thank you, Dan. This is the easiest question we've had all day. As modern cars go, the horn system is a very simple one.
Tom: Even for my brother! There's a horn pad on your steering wheel. When you press on it, you push together two metal contacts.
Ray: When those contacts touch, they don't make the horn blow. "Why not?" you say. "That's what happens in my car!" Well, yes, but there's an intermediate step you don't know about.
Tom: The horn takes too much current to safely run through your steering wheel, so those contacts in the wheel trigger a horn relay, which is just a heavy-duty switch that lives either under the dashboard or under the hood.
Ray: Then the relay closes and allows power to flow through to the horn itself (the noisemaking part of the system), which sits in front of the radiator.
Tom: So, one of those three components is not working.
Ray: Thank you, Steve McGarrett.
Tom: Start by checking the horn itself first. Old horns do rust out and fail this way. The easiest way to test it is — when the horn's not working — have someone try to honk the horn while you tap on the casing with a screwdriver or something. If you can get it to make any sound at all — even some sick-goose-like half-honking — that means your problem is in the horn.
Ray: And keep in mind that there are two horns that blow at the same time when you honk (that's what produces those two dissonant notes). It's possible that the first one died in, like, 2005. And maybe you've just now noticed that the second one is gone.
Tom: You also can test the horn more scientifically by hooking up a test light to it. If the test light goes on when someone honks the horn for you but the horn doesn't make any noise, then you know the horn is getting current and just isn't working.
Ray: If the horn is not getting current, then it's either the contacts in the steering wheel's horn pad, or it's the horn relay.
Tom: I'd bet on the relay first. Why? Because it's easier to replace a $20 relay than it is to take apart a steering wheel.
Ray: If a new horn relay doesn't fix it, then you know it's in the steering wheel, and you'll have to take it to a mechanic and shell out some money, Dan. Or go for that "add-on" horn button. Good luck.
(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk website.)