How The Check Engine Light Works
The computer knows what readings are in a normal range for various conditions. Get out of range, and it logs a trouble code and lights up the check engine warning.
The computer will then try to make adjustments if it can. If the computer can't compensate for the problem, the check engine light stays on.
The computer logs a trouble code. Some people think the code will tell the technician exactly what's wrong?
Actually, the code will tell the technician what sensor reading is out of parameters. It can't really tell you why, because there could be any number of causes.
Here is an example:
Let's say you're feeling hot. You get your heat sensor out - a thermometer - put it under our tongue and in a minute or two you learn that you have a fever of 104 degrees.
You know your symptom - a fever - but you don't know what's causing it. Is it the flu, a sinus infection or appendicitis?
You need more information than just that one sensor reading. But it does give you a place to start and narrows down the possible problems.
There are reports on the internet telling you that you can just go down to an auto parts store and get them to read your trouble code or buy a cheap scan tool to do it yourself.
There are two problems with that. First, the computer stores some trouble codes in short term memory, and some in permanent memory. Each manufacturer's computer stores generic trouble codes, but they also store codes that are specific to their brand.
A cheap, generic scan tool, like you can buy or that the auto parts store uses, doesn't have the ability to retrieve long-term storage or manufacturer specific codes. Our service center has spent over $80,000 on high-end scan tools and software to do a deep retrieval of information from your engine control computer.
The second problem is that once you've got the information, do you know what to do with it? For example, a very common trouble code comes up when the reading on the oxygen sensor is out of whack.
So the common solution is for the auto parts(Autozone) store to sell you a new oxygen sensor, which are not cheap, and send you off on your way. Now your oxygen sensor may indeed have been bad and needed replacing. But the error code could have come from any of a dozen of other problems and the service engine light comes right back on in a few days!
How do you know the right solution? Back to the fever analogy, do you need surgery or an aspirin? Leave it to the pros.
In closing anyone can scan a vehicle for codes and tell you the code and the possible part the code is referring to, but only a certified, experienced auto repair technician who lives and breathes auto repair can correctly diagnose the problem the first time and have you on your way.
At Professional Fleet Services we will diagnose your check engine light problems right the first time. You will never be told "start with a tune up and fuel injector cleaning then go from there" like many other shops will do. they never took the time to confirm which cylinders or injectors are not working.