There is not a single day goes by that we are not asked, “how much will it cost to put my car on “the machine” and tell me what is wrong?” Fact is, as much as I wish there were such a machine, there has been no such invention. However, we have many different machines and pieces of equipment that help aid us in the diagnosis of many of the problems that do exist. More on this in a moment.
    
I think that there are three reasons that many people think such a machine exist. 1st, the world in which we live is booming with so much technology that we just figure such a machine should exist. 2nd, about fifteen years ago a major tire retailer with stores across the nation that also does auto repair, began using a machine that gave a printer generated piece of paper that suggested what could be wrong with your car. When these stores showed you the print out listing things such as plugs, wires, distributor cap, vacuum leak, fuel system etc., they failed to point out the words “possible causes.” How many people have paid for these services that were not needed because this little piece of paper said so? 3rd, the biggest problem, consumers and auto parts stores with code readers.  A $39.00 device you plug under the dash and it tells you the problem. WRONG!!  If this were the case, these guys would be working in a shop and not selling the parts.

There is no machine that you hook up and it tells you what is wrong, no matter what the guy behind the counter tells you. Any honest shop or dealer will tell you the same thing.  It does not exist. If you could hear the number of customers that have purchased countless
parts that did not fix their cars, you would probably be amazed and know why they have these code readers, they sell parts that are not returnable after you install them. Reading a code and diagnosis are not the same thing.  Most late model vehicles are capable of setting thousands of codes with only one service engine soon light.  While it is true that once in a while you get lucky and the part you purchased fixed your car, more often you waisted time and money. The best example of this happens on a regular basis. Plug in the code reader and get an oxygen sensor circuit failure. You notice that I did not call it an oxygen sensor failure, it is an oxygen sensor circuit failure. Ask the auto parts guy how many of these he sells to individuals verses reputable shops. The numbers will probably shock you. Here is why. Yes, the oxygen sensor could be defective, however, in most cases it is only doing it's job by turning on the service engine soon light. Lets say you have a bad fuel injector, a leaky intake manifold gasket, a defective pressure regulator, a bad catalytic converter or any number of other issues that will affect the emmissions through the exhaust system, know what the job of the oxygen sensor is? To inform the computer that there is a problem down here so you need to turn the service engine light on so the the driver can have it diagnosed. Know what happens if the driver pulls out the code reader or gets the guy behind the counter at the auto parts to do it. You usually end up with a new oxygen sensor. Again, sometimes you get lucky if none of the above listed things are wrong with the car, however if any of these problems exist, you just get a new oxygen sensor telling the computer the same thing the old one did, maybe a little quicker because it is new. Funny how most people just say "well the sensor was old anyway, and they didn't charge me to check it out.' Thats because they are using a $39.00 code reader and not the thousands of dollars it cost for the other equipment, the experience, training, service procedures, diagnostic flow charts and hours (not minutes) of checking that is required to find the failure. Sometimes these cars come in after replacing as many as four of them because the same code keeps coming back and the auto parts store keeps selling them. I would say that for every ten oxygen sensor circuit codes that come in, we sell two sensors. Sure we could sell ten, but then that would make us parts salesmen and not technicians. Not to mention the fact that we would be wrong 80% of the time. That is why it sometimes cost as much for the diagnosis as it does for the repair.        

Hopefully this will help when you take your car into a shop and they can not give you an estimate until you allow them to perform the diagnosis.  Different circuits take different amounts of time to perform the test procedures.  Multiple circuit codes will usually mean more dollars because of more time spent to go through the diagnostic flow charts created by the manufacturer.  And last but not least, do not unhook your battery in attempts to reset the service engine soon light.  You may loose valuable information that could take several days or more of driving to gain it back before a diagnosis can be done. If you take your car to your mechanic with no codes, he will tell you to take it back and drive it for several days or pay him to drive it until the computer goes completely through it's relearn process. Remember, time is measured in dollars at any auto repair facility.                       Willy Ivy