Have you ever had an experience like this? You drive through the one of those automatic car
washes. When you get to the end, where the dryer is blowing, your check engine light started flashing!
You fear the worst, but within a block or two, the light stopped flashing, but
stayed on. By the next day, the light was off.
You wonder; "What was going on?" Well, it's actually a good lesson in
how the Check Engine light works.
Your air intake system has a sensor that measures how much air is coming
through it. When you went under the high-speed dryer, all that air was blasting
past the sensor. Your engine computer was saying, there shouldn't be that much
air when the engine is just idling. Something's wrong. Whatever's wrong could
cause some serious engine damage.
It flashes the check engine light, to alert you to take immediate action.
It stopped flashing because once you were out from under the dryer, the airflow
returned to normal. Now the engine control computer says the danger is past,
but I'm still concerned, I'll keep this light on for now.
Then the Check Engine Light goes off in a day or two.
The condition never did recur, so the computer says whatever it was, it's gone
now. The danger is past; I'll turn that light off.
Now a flashing check engine light is serious. You need to get it into the shop
as soon as possible. But if it stops flashing, 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 the engine. Things like alter the air to fuel mix, spark
advance, 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 range, and it logs a trouble code and lights up the check engine
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
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
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. We at Deerfield Tire Co. have spent a lot of money on high-end scan
tools and software to do a deep retrieval of information from your engine
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 store to sell you a new oxygen sensor, which are not cheap, and send you off on your way. Now it is possible your oxygen sensor may indeed have been bad and needed replacing. But the error code could also have come from any of a dozen of other problems. Which means the light will still stay on or return and you purchased a new oxygen sensor for no reason.
How do you know the right solution? Back to the fever analogy, do you need
surgery or an aspirin? Leave it to the pros at DEERFIELD TIRE CO.
Give us a call at 847-945-9550
and let us help you resolve your check engine light issue.
Proudly Serving The North Shore Since 1973