A Diagnosis Is…

Ok, many, many people, even so-called “mechanics” do not understand the process of troubleshooting a problem on a modern automobile. This little discussion is to help you, as vehicle owners understand what needs to be done during a diagnosis and why it is important for a professional to do that.

For the purposes of this discussion, a “Diagnosis” is referring to computer diagnosis or electrical testing, NOT a brake check, basic A/C check, noise check, etc.

Myth #1: The computer will tell you everything.

Fact: Not only no, but heck no. The car has an onboard computer that monitors the outputs of the sensors on the engine (input) and controls the components of the engine management system (output controls). The computer monitors all of these circuits and if one of those circuits is not performing as expected a code indicating which circuit has the problem is stored. The computer DOES NOT test the COMPONENT, nor does it test the wiring. The computer simply raises a red flag to indicate a value is not what it was programmed to expect.

Myth #2: (Insert Auto Parts Store Name Here) can do a diagnosis for free!

Fact: Performing a diagnosis correctly is difficult, requires extensive knowledge and training, expensive tools, and time to perform the needed tests. Access to very precise and accurate service information is also frequently needed. All that a parts store can do is retrieve the trouble codes stored in the computer. That is called “pulling codes” or a “computer scan”. That is NOT a diagnosis; it is the first step of the process of diagnosing a car. A parts counter worker does not have the ability to perform the rest of the steps to isolate the cause of a stored code. Also keep in mind auto parts stores make a profit by selling parts. They will be more than happy to sell you parts based on a computer scan, and if that doesnt’ fix your car, they do not care. Shops get paid to fix cars. We don’t get paid until we fix your car, which is a heck of an incentive to get it done right, on time.

Myth #3: It is cheaper just to ‘try’ a couple of things first than to pay for a diagnosis.

Fact: This gets more people in trouble than anything else. The situation now becomes complicated by that fact that someone not capable of determining the cause of a problem has tried to solve that problem. Quite frequently an inadvertent problem is caused that complicates the original issue. Diagnosing one problem is difficult enough, but doing it when someone else has complicated the issue with the installation of unknown quality materials or improper installation can be impossible. See myth #4 for an extension of this.

Myth #4: Putting on a new part eliminates that part as a possible cause of the problem.

Fact: So sorry, Charlie. I have a saying I stole from an unknown tech writer years ago. New is an acronym. N.E.W. Never, Ever, Worked. As many as 2% of brand new parts are non-functioning right out of the box, depending on the quality level of the part. If you cannot accurately test a part on the car, how do you know your “new” part works? Also, the parts store isn’t perfect. Sometimes you get re-boxed warranty defects that make it back onto the shelf. See above section about complicating things.

Ok, some tips:

A good Diagnosis will cost you approximately 75-150 dollars depending on the shop. A technician who is not being paid to perform that service is NOT going to spend time trying to be as accurate as possible. Keep in mind technicians are paid by productivity. They do not like to work for free any more than anyone else. Therefore, you must pay them for their time if you want the job done right. You get what you pay for. A free diagnosis at the auto shop is simply a gimmick to get you there. Once you are there they will either A: bill the time back in the job, or B: tell you if you want accurate testing, you have to pay for it.

Ask for and recieve the results of any testing performed in writing. Even if you don’t understand it, if there is a conflict, a professional will understand. Keep records. A good shop keeps all of that information on file for future use.

Ask before you approve: We don’t charge for the diagnosis if we can’t fix it. If you decline the repair, that is different, you are still responsible for the fee. Some shops charge no matter what.

Don’t expect to get the diagnosis for free if we do the work. The diagnosis is the expensive, time consuming part that requires the highly trained technician. Parts can be changed by people with much lower skill levels and usually without expensive testing equipment. Why would we give away the part that takes all of the tools and the talent? See tip about free diagnostic above.

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