How Your Check Engine Light WorksFebruary 27th, 2022
A flashing Check Engine light is an indication of a serious problem. You need to get it diagnosed as soon as possible. However, if it stops flashing then you can wait a few days, so you have time to see if the problem will clear itself or if you need to get it checked. How does the computer know when to clear itself?
Think of it this way. The engine control computer is the brain that can make adjustments to manage how your car runs and it monitors every electrical system in your car to make sure that the engine is running correctly. Things like alter the air-to- fuel ratio, timing and so on. The computer relies on a series of sensors to get the information it needs to make decisions on what to do.
The computer knows what readings are in a normal range for various conditions. Get out of the required range, and it logs a trouble code and your Check Engine warning light will come on.
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 him why, because there could be any number of causes.
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 40 degrees C.
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 internet websites and forums telling you that you can just go down to your local 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 online or that the auto parts store uses, doesn’t have the ability to retrieve long-term storage or manufacturer specific codes. Your local service centre has spent a lot of money 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 parts store to sell you a new oxygen sensor — which is 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.
How do you know the right solution? Back to the fever analogy, do you need surgery or an aspirin? Give us a call and let us help you with some friendly advice on how to resolve your check engine light issue.
PO Box 16686, Hornby, Christchurch
New Zealand 8441