Ray's Extra Smart Scan Tool

Aug 08, 2005

RAY: At our shop, we have a scan tool. This tool is designed to plug in under the dash or under the hood of the car and extract valuable information from the car's computer.

TOM: So we can misdiagnose the problems!

RAY: Exactly. Recently, we got a new piece of software for our scan tool. One of my guys had plugged the scan tool in, and was looking for readings that indicated a problem. For example, if it says the engine operating temperature is minus 40 degrees, you have some idea that there's something wrong with the engine's temperature sensor.

He was scrolling down and looking at all the information, when he came to a reading that said, "air pressure low right, front tire."

He said, "Huh?!" So, I walked around to the right front tire and sure enough -- the tire was almost flat and I said, "It's right."

The question is, how did the scanning tool know that the right front tire was low on air?
RAY: We all know that when a tire loses its air it gets smaller. And if your car had a device that could measure how much the car was tilting, it could in fact tell you if it was tilting towards the right front, it could tell you in fact that it was the right front tire that was low. But unfortunately --

TOM: It doesn't have such a device.

RAY: But when a tire loses air pressure and its diameter gets smaller, when the car is going down the road, in order for that tire to keep up with all the others and not get left behind, it has to turn faster. And your car does have something that is constantly monitoring the speed of all the wheels and comparing them to one another.

What most modern cars have is ABS-- antilock brakes. And there's a sensor at every wheel that's reading how fast each of the wheels is turning. So, if it notes that the right front wheel is going a heck of a lot faster than the other wheels, it can either assume that you're making a lot of left hand turns or driving around a circle...or that your right front tire is going flat.

Who's our winner?

TOM: The winner is Jean Sager from Wessington, South Dakota.

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