"Check Engine" Light Came On. What Could It Be?

Hi, I have an old 1991 Hyundai Excel. The engine light came on during
the last 1/2 mile on my way home last night. What engine parts could be
screwed up? Would the light be telling me I have a problem with low oil
or low water or would that have it's own designated light icon?

 

Could be a lot of things. Did you just get gas? If so, the gas cap may be
loose and that can give a signal. If that is the culprit, it will take
about 15 or 20 starts to go away after tightening the cap.

Oxygen sensors go bad also. Very common cause. To know for sure, you have
to use a computer for readout of hte information. The car is still drivable
as is, but there may be long term effects if you don't get it check out soon
to know for sure what the problem is.

 

This happens to me all the time after getting gas if I don't tighten
the cap enough.

('99 Accent GSI)

Goes off after a few days fo driving after tightening the cap.

Chris

 

Pamela's car is pre-OBD-II, so the fuel cap idea is out.

The computer has no way of monitoring the oil level, so that's out, too.

It's possible the coolant is low and you set a code for the coolant
temperature sensor because the temperature got too hot.

Realistically, I'd need to know the trouble code to give you a good idea
of why the lamp may be on. What it means is that the computer has
detected a problem with the fuel management system.

If you've got an analog voltmeter, you can try to read the trouble codes
yourself. Go to www.hmaservice.com (requires Internet Explorer) and
register for a free account. In the shop manual for the 1991 Excel, there
will be an explanation of how to read the codes with a voltmeter.

If you're unable to read the codes yourself, you should take it to a shop
capable of reading the trouble codes. The dealer will be able to do this.
If you're considering taking the car anywhere else, call first to see
whether they can read the trouble codes on the car. Since it doesn't use
OBD-II diagnostics, many shops won't have the tooling required to do this
type of diagnosis.

 

Thank you all so much for the info! I didn't drive it all day yesterday
after seeing the "Check Engine" light come on the previous evening, but
today I started it up and to my shock the "Check Engine" light didn't
come on!!

I don't know why it didn't come back on but it sure is alright with me!!
And it never came back on the whole afternoon I was driving it. I
suppose it will appear in time so I'm going to find a mechanic with the
computer stuff that can diagnose it

Hyundaitech, thank you for the details on how to get the codes (I'm
going to save that for future refference), but I wouldn't know the
difference between a voltmeter and a muffler bearing!! Ha!! I just
recently finally found the transmission dip stick!! That little sucker
sure is hidden! Really, it's almost _under_ the engine!

Would you happen to know how long it should take a mechanic to actually
run that test on my car? I mean, could I drive it in and within an hour
have the results, or would I have to leave it all day for them to keep?
Reason being, I wonder if I'd need to rent a car for this situation.

 

When I had an oxygen sensor go bad, the light came on, went off, came back
again, off again, then finally stayed on. Since car don't repair themselves
it is a matter of time for it to come back.

As for how long it takes to get the codes, if the mechanic can do it right
away, it is only minutes. The problem is, most will not just drop
everything to pull your car in to check it on the spot, but will want you to
eave it for some time. Once the problem is determined, it could be minutes
or hours to get the part and replace it. That, of course, varies at each
shop.

 

Pamela

If your "Check Engine" light is not on, the mechanic will not be able
to read the error code, as there isn't one.

Chris

 

The computer holds the codes for some period of time.
http://autorepair.about.com/cs/generalinfo/l/bldef_154a.htm

 

I stand corrected.

Personally though, if the light has gone out by itself, I'm not paying
someone $60 to find out why it was on.

Chris

 

I probably wouldn't either for a one time deal. There are times that the
light will go on and the "problem" is corrected by a fresh tank of gas or
some outside source like that. OTOH, engines don't repair themselves so if
it does come on repeatedly, it will eventually need fixing.

 

Again because of your car's age, the check engine lamp works a little
differently than it does on most of the newer cars we discuss here. In
many cases, if the problem isn't present when you start the car, the lamp
will stay off until the problem reoccurs. The trouble code should remain
in memory for something like 50 key cycles, though.

A good shop (with the required tools) should be able to have the trouble
code for you within several minutes. The problem is that it may require
significant investigation to determine why that code set. You're best off
to plan on all day and be pleasantly surprised if it's quick than to try it
the other way around.

 

That is your choice, but keep in mind that some failures can cause
expensive damage, in particular damage to the catcon. If you'd rather
spend $800 to replace the catcon than $60 to find out which sensor is
getting flakey, that is your choice.

Matt

 

I guess I'm hesitant to shell out the cash for a check engine light
that has gone off on it's own accord considering that this happens to
me at least once every few months if I don't crank the gas cap after
filling up.

Older cars are different so maybe it's worth it.

Chris

 

I've never had the gas cap set off my MIL light, but then I don't find
correctly installing the gas cap to be that hard.

If you are sure that something like that is the cause, then I agree it
is wasteful to spend the $60. However, if something else is wrong and
you are dumping too much fuel into the engine, you can easily toast the
catcon and that is a very expensive repair generally.


Matt

 

I know you don't believe me but if I don't turn the cap til I hear like
12 clicks, the light will come on. Is the problem my gas cap? Would a
new gas cap solve the problem?

Chris

 

Yes, I would think something is defective with your gas cap. I turn
mine until it clicks and then stop. I probably get 2-4 clicks just from
inertia, but I don't attempt to turn it beyond the first click that I
hear. If the cap isn't cross-threaded, it shouldn't take more than a
one click to seal as the torque should not increase behind the first click.

Matt

 

You pump your own gas? Sorry to hear that. In NY and parts of MA it is
forbidden to pump your own. Funny thing is, the full service is cheaper
than most self serves. This (pump yourself and save) is the biggest scam
ever foisted on the driving public.

Self serve in my town in CT is 2.579, but I bought full service in MA today
for 2.329. It is probably even cheaper in NJ. Last time I was there I paid
1.939. I'll be damned if I'm going to freeze my ass off and pay more for
the privilege.

 

The reason gas is cheaper in NY and NJ has much more to do with the state
gasoline tax than who is pumping. I'd be interested in seeing a
cost-comparison chart by state if we normalized the data to remove taxes.
Unfortunately, I'm not up for spending the time to put it together.

 

Actually, I prefer to pump my own gas just as I prefer to change my own
oil. That way I know that the gas cap was replaced correctly and the
drain plug for the oil likewise.

It isn't forbidden to pump your own gas in NY. I live in PA and work in
Corning, NY and they have lots of self-serve stations, actually I only
know of one or two that still pump gas for you. Maybe you are thinking
of NYC.

Full-serve, where available around here, costs 2-5 cents per gallon more
than self-serve. Why do you think it is a scam? Do you think the
person pumping the gas is working for free?

That certainly isn't the case around here. I don't mind pumping my own
even at below zero temps. Maybe you should move south where it is
warmer.


Matt

 

In MA, each town fire marshall determines if the motoring public can safely
pump their own gas. In the towns that are full service, the price is the
same, sometimes a penny or so cheaper, than the self serve. They still
manage to pay that (usually a high school kid) pump jockey a wage and make a
profit. In my CT town, the self serve is competitive, but if you want full
service, they charge you 20¢ a gallon more for the kid to come out and pump
for you. They are really saying they don't want to do it. That is a scam
if the guy up the street can pump it for the same price. We were told by
the big oil companies that they were offering self service as a cost benefit
to the buyer. The fact is, they kept the self service price the same and
artificially raised the full service price well beyond what it should be. ,

No reason to move; too many bugs in the south. I just have to be thoughtful
as to where I buy my gas. In 45 years of driving, only once was the cap not
tightened properly. The town where my office is has self service, but the
next town over where the warehouse is, has full service at the same price or
a penny less. So, I just buy my gas the next town over when I go there.
Keeps those kids out of trouble and they can earn some beer money.