So my car has had the Check Engine light on for the last 2 weeks. It runs fine and I have a feeling it's just the light itself that's broken, but it made me wonder, what is this mysterious engine light? What does it actually measure? The fule gauge checks the fule, the spedometer measures the speed, but what is the "Check Engine" light actually indicating?
The Check Engine light can signal a number of different conditions which indicate operating conditions not condoned by the manufacturere.
In many cases, a sensor will deteriorate, and the light will come on. It may not mean instant disaster, but it signals a condition which needs to be addressed.
Read the codes stored in the OBD system. Then work toward a solution.
Poster reminds me of a saying my dad used regularly. It goes, "The wish is father to the thought." No Virginia, check engine lights do not often break and turn themselves on. You might get away with putting black tape over the light or you could just as well find yourself staring at that light as you sit along a dark road some rainy night.
The check engine light is connected to the car's engine fuel management computer, this is the computer that runs the fuel injectors, reads the engine sensors, etc. The O2 sensors are used by the ECM to determine how accurately it's injecting the fuel, and adjusting the way the fuel is injected to compensate for changing conditions. When the software/programming inside the ECM detects that there is something wrong, for instance a bad sensor or engine operating parameter that exceeds a preprogrammed set point then the ECM turns on the light to let you, the driver, know that something is wrong and needs to be attended to. The light itself is just a bulb, it's nothing more than just a bulb, but the function is critically important.
JazzMa
The oil light is not "attached" to the oil to see if it's full or not, although it will come on if it's low enough. The common red "Oil Light" is for oil pressure. Some vehicles do have a "low oil" light which will be, in most cases, amber.
The cause of a "permanent check engine light" is an owner/operator who refuses to repair their vehicle, not becuase the car is old.
Steve
It can signal a variety of potential problems. On many cars if the gas cap isn't screwed down tight the air leak will trigger the check engine light. Since the light has been glowing continuosly for two weeks now, I would get it in to a dealer pronto to have the error codes read and the problem corrected.
I think you are looking for a simple answer, and it isn't that simple. The engine control module, usually, monitors a number of different parameters, not just one. Sensors provide inputs to allow the computer to optimize the performance and emissions of the engine.
If any one of those sensors transmits a signal to the computer which is sufficiently off specification, the Check Engine light can come on. An error code will be set in the computer which can be pulled up and read using a scan tool (or in some older cars, the flashing readout can be initiated with no tool at all). Reading the stored codes can help you trace the problem. N.B.! It does not necessarily tell you which part to replace, but tells you what condition it has sensed. Given that information, you can run further tests, and/or work through a fault code decision tree to help localize the source and cause of the error.
In tough cases, the Check Engine light may be set by phantom codes. Something, like a short circuit or a voltage spike, may set a false code. There may not be a problem at all. In cases like these, you could spend half your life and lots of money trying to find how to get the damn light off. Many people just dont do it.
Like they say, the light is turned on by the car's computer. It's just an indicator that some computer reading isn't right. You have to consult the computer to find out what it's complaining about. To do that you have to plug in a device which can display the code or codes stored in the computer's memory. Then you have to look up the code or codes in a manual (or possibly somewhere on the Internet) to see what they mean. I have a Haynes manual for my car which lists the computer codes and what they mean.
You used to be able to read the codes by getting the computer to flash the check engine light and count the numer of flashes. On some cars you could connect an (analog) volt meter and count the number of ocillations of the needle. I don't think any newer cars can do that. You have to have the plugin display. My car is old enough that it does both the flashy and wavy things, athough the light has only come on once.
On some cars there's a way to turn off the check engine light if it bother you. I think on all cars disconnecting the batter under the hood will erase the computer's memory and that turns off the check engine light. But in both cases it's probably only for a short time because a persistent problem will keep turning on the check engine light.
( snipped-for-privacy@kcls.org) writes:
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Last time I had a check engine light come on, it was from a faulty crankshaft position sensor. But it could be caused by any number of engine "faults"
which word don't you understand?
By Jove, I think you have hit on it...
It may "run fine" but the computer has detected a fault in the system somewhere. The year of the vehicle makes a difference on what the computer monitors. On pre 95 vehicles with OBDI it monitors a throttle position sensor, ignition module, MAF or MAP sensor, O2 sensor, fuel injection system, transmission shifting and pressure, electrical system output, and a few dozen other items. ANY of them can generate a fault and activate the light. On newer vehicles you can add in MANY more sensors and even tighter control. If the light is on you have a problem, you may not think so but you do. You need to either have the codes read and do the repair yourself OR take it to a shop and have them repair it.
As far as vehicles that have the check engine light on just because of age, NOT true. That light is on because of a problem that those people just don't bother to repair because "It runs fine and I have a feeling it's just the light itself that's broken". In some states that light being on is an automatic failure on the safety inspection, so it becomes either repair it or park it.
In some states that light
How true. I had an 88 Subaru Justy with around 150,000 miles, that developed a "check engine" light. The first time it came on was as I rolled into a California smog inspection station. I was told by the mechanic that he wouldn't do the inspection with the light on. Fair enough. As I tried to find what the light meant (you could read the dashes and dots on a LED), the "check engine" light went out. Several days later, I went back to the inspection station. Guess what: the "check engine" light came back on. At that point, I discovered (from the inspection station mechanic; what a help) what the LED code meant: a bad altitude sensor. That meant that I might have trouble going up mountains and things! Though I had no desire to drive the Justy up a mountain, I had to fix it to complete my inspection.
When I checked with the local Subaru dealer, I found that replacement of the altitude sensor (including, I believe, all the tests to verify what I had found as the problem) would cost a couple of hundred dollars.
At that, I visited my local junk yard (yes, they still exist) and found a Justy altitude sensor for $10. Which I installed.
And passed the smog inspection.
Jim Thomas
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