Air-conditioning a likely culprit

Dear Mike: I have a 1999 Oldsmobile Intrigue GLS. On really warm days some type of moisture comes to the surface of the dashboard above the driver-side airbag.

Do you have any idea what the problem is?

A: Almost certainly this is condensed moisture from the air-conditioning system. The temperature of the moist air inside your car is lowered below the dew point, the humidity goes to 100 percent, and you have water. Some vehicles will blow little clouds out of the dash vents on humid days. Apparently, your car lets water collect on the dash. This is more common in, say, Florida and Mississippi than in drier places like Arizona and New Mexico.

Running the air-conditioning system on “recirculate” instead of bringing in fresh air will minimize this because you’ll eventually lower the humidity inside the car enough to keep moisture from condensing into liquid form.

Dear Mike: My “check engine” light came on last week, so I took the car to the auto shop and the mechanic changed the oxygen sensor. But he didn’t clear the trouble code from the computer, and the light stayed on for three days before going out.

Is the code still inside the car computer or not? When it’s time for inspection, is my car going to have a problem passing the emissions test? Is there any way I can clear the code myself without an expensive scan tool?

A: Obviously, the mechanic should have cleared the code. However, it’s supposed to clear itself after a few engine driving cycles, and it apparently did. Fine. You could have cleared the code yourself by pulling the computer’s fuse for 30 seconds. The code won’t come back unless the problem does.

Warning: If you are trying to pass a state emissions test in the near future, give the car a day or two of normal driving after clearing codes to allow the computer to go through its normal self-test cycle. If you don’t, the scan tool at the DMV will show that there’s a problem, and you’ll get a rain check to come back and try again. (So, no, pulling the fuse while waiting in line to see if you can pass before the light comes on again won’t work.)

Dear Mike: I am the (once proud) owner of a 2006 Ford F-250 pickup with the 6.0-liter diesel engine. The truck has only 8,900 miles on it and the “check engine” light has already come on twice. Both times the cause was a defective “fuel pump module,” repaired under warranty.

I was told that if I add any more fuel after the pump nozzle’s first click when I fill the tank, I am adding too much pressure to the tank; hence, the module is overwhelmed and goes bad. Yes, I even out my purchase prices, but I never keep filling the tank to the point that diesel fuel spills out past the nozzle. The service writer’s explanation sounds weird.

A: Sounds pretty strange to me, too. The standpipe from the filler neck into the tank is placed so that there is an inch or more of free space above the fuel on any modern vehicle. This space provides room for the fuel, which is typically stored in cool underground tanks, to expand as it warms up in the tank without overflowing onto the ground. The service writer is talking through his hat.

.