Check Engine - question

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?

> wrote in message
ups.com...
> 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.

I've seen many cars that had a permenant CHECK ENGINE light on after
the car gets older. But my point, or question is, what is that
"attached" to, what is it measuring. The Oil light is "attached" to the
oil to see if it's full or not, but what is the engine light "attached"
to?

Al Bundy wrote:
> 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.

wrote:
>
> I've seen many cars that had a permenant CHECK ENGINE light on after
> the car gets older. But my point, or question is, what is that
> "attached" to, what is it measuring. The Oil light is "attached" to the
> oil to see if it's full or not, but what is the engine light "attached"
> to?
>

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
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> "attached" to, what is it measuring. The Oil light is "attached" to the
> oil to see if it's full or not, but what is the engine light "attached"

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

wrote:
> 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?

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.

> wrote in message
oups.com...
> I've seen many cars that had a permenant CHECK ENGINE light on after
> the car gets older. But my point, or question is, what is that
> "attached" to, what is it measuring. The Oil light is "attached" to the
> oil to see if it's full or not, but what is the engine light "attached"
> to?

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.


) writes:
> 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?
>


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William R Watt National Capital FreeNet Ottawa's free community network
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Thank you, I didn't realize it was actually stored in a computer.
That's good to know.

William R. Watt wrote:
> 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.
>
>
> ) writes:
> > 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?
> >
>
>
> --
> ------------------------------------------------------------------------------
> William R Watt National Capital FreeNet Ottawa's free community network
> homepage: www.ncf.ca/~ag384/top.htm
> warning: non-FreeNet email must have "notspam" in subject or it's returned