Computer scanners, sub-frame damage, higher octane mileage

By John Paul, AAA Car Doctor
September 4, 2008

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Q. What do you think of inexpensive computer scan tools? I do some of my own repairs and would like to be able to diagnose check engine light problems.

A. Professional technicians use manufacturer specific scan tools. These tools will allow in depth diagnosis and have the ability to control functions of the vehicle. Simple code readers will allow some basic diagnosis and have the ability to clear check engine lights. I was recently reading about a tool from Black and Decker. The tool is called SmartScan and promises quite a bit and retails for less than $100. I am waiting to test one.

Q. I have read that you have said that there is a fuel savings by using premium fuel in a car that requires it. Your argument is that you pay more at the pump but less in overall fuel cost because with lower octane (cheaper) fuel you get less miles per gallon. I have read recently that is not the case. Do you still think this way?

A. My experience has been that the 20 cents you pay more for premium is offset in the overall miles per gallon. This may not be the case for every car and engine design. Using lower octane fuel will result in less power. If you don't care about the overall performance of the vehicle and your car is a late model you can get away with 87 octane. Although, I would do the math and see if it makes financial sense.

Q. We were recently in an accident where the front transmission pan and the sub-frame had to be replaced. What is this sub-frame damage going to do to the value of this minivan?

A. If the van was repaired properly there should be no change to the value of the vehicle. It is when repairs are performed in a shoddy manner and the vehicle is not returned to its pre-crash condition that the value and possible safety of the vehicle can be called into question.

Q. My "check engine" light came on the other night and the engine is sluggish. It doesn't accelerate normally; I need to put my foot flat to the floorboard to get it going. Now the "check engine" light has turned off and the car is running OK. What do you think the problem could be?

A. You need to start with a check of the vehicle's on-board computer system. The "check engine" light came on because one of the many computer sensors detected a problem. Rather than guess at the problem, have the computer scanned for codes as well as a basic check of the fuel and ignition system.

Q. I recently purchased a 2000 Toyota Camry from someone at work for $4,600. I repaired the front and back brakes, and changed the oil, PCV valve, air filter and spark plugs. I also had the fuel injectors cleaned, yet I can't get rid of a big problem. Every morning when I start the car in the morning, it starts and dies. Without exception, if I try to restart immediately after, it starts and runs fine all day. Even if I stop and start many times during the day it runs fine. If is just the first start when there is a problem, what could be wrong?

A. There are two items to take a look at. The idle air control motor could be a problem, not allowing the idle to speed up, or the engine temperature sensor could be faulty. If the temperature sensor "thinks" the engine is warm, even when it is cold, it will start and stall. A computer scan tool will help the technician pinpoint this problem.

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


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