DEAR CAR TALK: Sometimes when I go into my garage late at night, I can hear a humming noise coming from my 2005 Tacoma. It sounds like a small electric motor running. What is it and will it eventually run down the battery?
— Randall
DEAR READER: What's it humming? If it was a German car, it would probably be "Ride of the Valkyries." I'd be curious to know what Japanese trucks hum.
What you're hearing is the evaporative emissions pump. In the old days, fuel systems were vented directly to the outside air. Every gas cap had a hole in it to let the gasoline vapors escape. But that was a huge cause of smog. So fuel systems were redesigned and sealed to trap gasoline vapors. Inside a sealed system, we now capture gas vapors in a charcoal canister and then reintroduce and combust them when the car starts up again.
What you're hearing is a pump that pressurizes your fuel storage system (the tank, filler neck, gas cap, evaporative canister) in order to test it, and make sure it's sealed. As long as the system holds its pressure, the computer concludes that everything is fine, and it stands down.
But if the system can't hold pressure — if the pump has to come on too often or for too long — then the computer assumes there's a leak from which gasoline vapors are escaping, and it will turn on your check engine light.
So if your check engine light hasn't come on, there's nothing to worry about yet, Randall. If it HAS come on, first check to be sure your gas cap is on tightly and correctly. That's the single most common source of a fuel system pressure leak. And if that doesn't turn the light off in short order, you've bought yourself a trip to the mechanic to figure it out.
Either way, stop sneaking up on your truck like that in the garage, Randall. Give it a little privacy at night, eh?
DEAR CAR TALK: I drive a supercharged 1994 Buick Park Avenue Ultra with 123,000 miles. The horn quit working, and I took it to a Buick dealer who ran a diagnostic test.
Their test didn't show why the horn had quit working. They thought it might be a short circuit. They offered to do a more extensive test for $375 but would not guarantee that they could find the problem.
I did not take them up on their offer. They suggested that I try to find a Mom and Pop car shop that would do the diagnostic work more cheaply. No luck so far. Do you have any idea why the horn quit working?
— Jerry
DEAR READER: I do, but I'll have to charge you $375 before I tell you.
Actually, no. I don't know. I'm guessing the dealership ran the simplest tests. They probably started by checking the fuse and horn relay. Those take about two minutes each. Then they energized your horns (there are two of them, which is what creates that obnoxious, dissonant musical note) and found that the horns themselves worked fine when properly energized.
Then, they probably tested the wires that attach to the horns and discovered that there was no power arriving there. That means that the problem is somewhere between your palm and those final horn wires.
That's how we would have started, too. And the truth is, at that point, the work starts getting a lot more time-consuming, which is why they quickly lost interest.
If I were working on your car, the next thing I'd check is the horn pad on your steering wheel, given the age of your Buick. Checking that requires removing the horn pad, which contains the driver's airbag. Once you remove the horn pad, you can jump the horn wires and see if that makes the horn blow. If it does, then you need a new horn pad.
If jumping the wires doesn't sound the horn, then you've got a wiring issue — somewhere downstream of those two wires and upstream of the horns themselves — and that could easily run into several hours of labor and, therefore, hundreds of dollars to track down.
Alternatively, if you're ready to accept that this car has officially entered heapdom, you could bypass your current setup and have a shop install a new horn button somewhere that's easy for you to reach on the dashboard.
For less than $100, someone could probably rig up a nice, big, red button that you can't miss, that's wired right to the horns. Sure, it's not elegant. But elegance could easily cost you $300-$400.
Good luck, Jerry.
Ray Magliozzi dispenses advice about cars in Car Talk every Saturday. Email him by visiting cartalk.com