Horn spontaneously honking in winter temps.

Dear Car Talk

Dear Car Talk | May 01, 2003

Dear Tom and Ray:

The temperature in my Minnesota town at 3 a.m. last night was minus 20 ... which was still not as cold as the letter of rejection I recently received from Harvard's Graduate School of Education. But I digress. At 3 a.m., I, along with others on my block, awoke to the blowing horn on my girlfriend's 1991 Mazda Protege. This is the third instance when the car's horn sounded at an odd hour of the night, and it doesn't stop until the car is warmed up and has been running for 20 minutes. After breaking my pen in a mad attempt to pry random fuses from the fuse box, I discovered that the horn fuse also powers the brake lights. So, removing the fuse is not a good option. What's the deal? -- Dave

TOM: I think it's your girlfriend's father, Dave. He's out there leaning on the horn.

RAY: There are two possibilities, and they both have to do with cold weather. Things shrink when they get cold, Dave. It's possible that during the coldest part of the coldest nights, your horn relay is closing on its own and making the horn blow.

TOM: The horn relay normally gets closed when you push the center pad on your steering wheel -- the relay then activates the horn under normal circumstances. But when relays get old, they can close by themselves. The relay is located under the dashboard, to the left of the steering wheel. So, the next time this happens, reach under there and start pulling out relays until the noise stops. Or, if you'd prefer, you can go buy a new horn relay for about $10 and pop it in there in advance.

RAY: If a new horn relay doesn't fix the problem, then it's probably the horn pad that's shrinking in the cold and completing the circuit. The horn pad on your steering wheel is separated from the contact ring by four little springs. Those springs might have worn out over the years, or it might just be so cold that the plastic horn pad itself is shrinking enough to make the contacts touch.

TOM: You can pop off that horn pad with a screwdriver, and you can probably find replacement parts at a junkyard. Just don't leave the car unattended, though, Dave. They might mistake it for "incoming."

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One