Check engine light

[BobT]

1997 Pontiac Bonneville with 3800 engine.

Early last week my daughter told me that the diagnostic system "Check Engine" light came on. I asked if the car seemed okay otherwise and if her oil pressure, temp, and other gauges were showing normal positions. I expect that the diagnostic system would also have indicated if any of these were not within parameters but I had her look anyway. Nothing seemed out of the ordinary but the light remained lit.

With my Ford vehicles, if the system detects something it will remain latched for at lest three start cycles so I told her that we would keep any eye on things but she was to tell me immediately if the car's performanced changed in any way. After about three days of driving to school and work the light went out. We drove down to Granite Falls yesterday so I decided to use the car to see if everything seemed okay. No problems at all. This morning she called and told me the light came on and when she turned the car off and back on again, it went back off, which seemed a bit curious to me.

According to the manual, there are three situations that may cause this that the end-user might be able to diagnose himself.

* Loose fuel cap.

* Going through deep water where electronics could have become wet from water spray.

* New fuel source where there could possibly be something different about the fuel.

Aside from this it only suggested that a mechanic should be contacted to connect online to find the applicable code.

How important is it that I bring it in? Is it best to do it now or can I wait until the next oil change and have it checked then? The car seems to be performing just fine otherwise.

[Jack Peterson]

More often than not on late 90's GM cars it's a code P0440 which is a fuel system leak. Often taking the cap off (like you said) and putting it back on might solve the problem, but taking it in to get checked never hurts. A mechanic will have to clear the code with a scan tool.

I don't know what other shops charge for scanning a vehicle, but I know when I change oil and someone asks to clear the codes for the check engine light, I usually don't charge anything.

If it's running fine, I would just watch it carefully until the next oil change or service due.

Jack.

[DTro]

Yep, go to a parts store and borrow a scan tool to at least give you an idea what triggered it.

I've had bad EGR valves that showed no noticeable drivability issues.

[Jeremy airjer W]

With that type of on and off activity I would almost guarantee it is an 02 sensor or as DTRO suggested an EGR valve code. This doesn't necessarily mean these are bad but the PCM has detected that they are out of there parameters.

The best thing to do is find out what the code(s) are and work from there.

[BobT]

Does this sound like something I shouldn't wait to have checked or will I be safe for now. There's a couple thousand miles left on this oil so I'm not expecting an oil change for a while.

[Jeremy airjer W]

I had a customer who had a newer toyota that ignored a check engine light for over 4 years until the vehicle started running rough and the light started to flash. The light flashing was letting us know there was a misfire which a simple tun-up took care of. The reason the light had been on for over 4 years had to do with the charcoal canister. The manufacturer recognized there was a problem with the design and extended the warranty on them to 8 years or 160,000 miles. Four years ago he would have been in the warranty claim parameters and would have had the part replaced for the cost of diagnosis. Instead he paid over $800.

It's always best to at least find out what it is as soon as possible. Then decide whether or not its a priority and when to fix it.

[Jack Peterson]

If you have a couple thousand miles left, you might as well take it in for a winter/cold weather check over, and have your mechanic check out the codes.

There are a wide variety of codes that could be setting off the light, but more than likely it is one of the more "simple fix" codes that have been stated in this thread.

Although, I've seen cars come in with a misfire and we've replaced the plugs and wires only to find out that the head/intake gaskets needed to be fixed as well.

Never hurts to bring it in sooner rather than later, because a minor problem can bring light to a bigger problem.

[BobT]

Thanks. Will do.

[DTro]

I think this might be an older OBD? You might be able to read the code with a simple jumper wire/paper clip and the dash light.

[spearchucker]

Take it to an Autozone or O'Reilly's. They will read out the code for free. At least you will know what your are dealing with. You can always take it in for repair or do it yourself if you are comfortable.

[ottertailguy]

My chevy check engine light came on a year ago after I fueled up. I was an [PoorWordUsage] and over filled it and the gasket must of dried out from gas. I talked to a friend and was told to rub a little oil on that rubber gasket on the gas cap. Sure enough the light went out right away and never came on again. You can try this first if you want.

[Jeremy airjer W]

95/96 was the crazy year switch from OBDI to OBDII for GM. This (97 and later) will be OBDII and you will not be able to jump the A & B connectors to retrieve codes.