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THE CAR DOCTOR

Slow down before you start fixing computer bugs

Plus: SUV alternatives, inspection stickers

By John Paul
Boston.com Correspondent / December 1, 2008

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Q. I have a 2000 Monte Carlo SS with a 3.8 liter V-6 Engine. My problem is this: Every so often we lose cold air from the air conditioner and the water temperature gauge goes back to cold. However, if I unplug the battery cables for an hour or so and reconnect the cables to the battery, cold air blows and the water temperature gauge works fine. This problem may not happen again for several months, yet it might happen again in as little as a few days. It seems this occurs when I drive this car at around 90 to 95 miles per hour. I have taken my car to have it hooked up to a computer and no one has been able to resolve this issue. I was told it sounded like a bad heat sensor, so I replaced that myself and I thought the problem was resolved - until today it happened again. Help.

A. Start by slowing down. By disconnecting the battery you are "rebooting" the car's computer. Additional testing will need to be performed and the repair could involve replacing the body control computer.

Q. My 1991 Honda Accord ran fine until suddenly the green S on the dash started to flash. The car would not shift out of first gear and the speedometer didn't work. My mechanic said he fixed a short to ground in the Vehicle Speed Sensor. The car ran fine for about a day, and then the exact same thing happened. I couldn't get to the mechanic right away so the car sat for about two days. On the way back to the mechanic the car ran great but the S started to flash again. The mechanic will take a look at the car tomorrow. I suspect the VSS needs to be replaced. Any ideas?

A. The problem may be a faulty transmission control computer. There is a resistor in the computer that burns out and fails, causing the transmission not to shift.

Q. My husband just changed the valve cover gaskets on my 1996 Mazda MPV. When he finished the job and started the engine, the "check engine" light came on. Do I have to go the shop to turn it off? What do you suggest we do?

A. Have your husband recheck his work; he may have left a vacuum hose or electrical connector off. If he finds a problem, disconnect the battery for a few minutes. This will shut off the light and clear the computer code. If everything appears to be attached then the van will need to go to a repair shop to determine the source of the "check engine" light.

Q. I have an 1989 Honda Accord four-door. I gave my car a tune-up about two months ago. Ever since then it has been hesitating more often when accelerating. Recently it has started to make noises and stutter really badly. What did I do wrong in the tune-up? I'm trying not to take it to a professional because I don't have the money. Any answers?

A. During the course of the tune-up you may have damaged a spark plug wire. With the engine running, use a spray bottle and mist some water on the spark plug wires. If you see sparks jumping, you have found your problem.

Q. I recently purchased a used car from a local suburban Boston dealer. I was surprised the car needed an inspection sticker. When I asked the dealer about this he told me they did some engine repairs and that I needed to drive 100 miles before it could be inspected. Is this true and isn't it illegal to drive without an inspection sticker?

A. Before a car can be inspected, the computer needs to set trip "monitors." These monitors ensure the car has gone through complete drive cycles, testing and retesting the various sensors, verifying that all systems are working properly. In some cars this can take up to 100 miles. Massachusetts law requires that when purchasing a car it needs to be inspected within seven days so you should have time.

Q. I am looking for a new car, preferably a station wagon with four-wheel drive that handles well. Decent fuel economy is a must. I currently drive a Jeep Cherokee Laredo and it drives like a truck. What do you recommend as an alternative to rough-riding SUVs? I do not need off-road handling, just something that handles snow. I am thinking about the following choices: Volvo XC70, Subaru Outback or Forrester and the Volkswagen Passat Wagon. Which would you recommend?

A. The Volvo, Subaru and Volkswagen are all good choices. The Volvo XC70 delivers the best combination of safety, handling and prestige - although fuel economy will only average in the mid-teens around town and in the low 20s on the highway and it does require premium fuel. The Outback would be my second choice; it's solid and reliable.

John Paul is the public affairs manager for AAA Southern New England. He can be reached at jpaul@aaasne.com.