Car engine light on; mechanic can't find anything wrong

My husband’s car is a 2000 Hyundai Elantra station wagon with 135,000 miles on it. He has had the appropriate maintenance done on it. Recently he noticed that the “check engine” light stays on the whole time he’s driving. Our mechanic can’t find any problem. Hubby was using it for a 45-minute commute to work, but now is worried about doing that, so he uses only occasionally for short runs near home. (He’s now working close to home and is using his pickup truck for his commute.) He seems to think that the car’s usefulness is over because of the high mileage, and is considering getting rid of it. I say we get it fixed, but the closest Hyundai dealer is 45 minutes away and he doesn’t want to chance driving it that far. I suggested we find a mechanic nearby who specializes in foreign car repair. Can this car be saved?

My suggestion is get a new mechanic. A computer needs to be hooked into it to identify why the light is coming on. The car tells him. There is a reason for it going off. It isn’t necessarily anything important, so inspecting the engine will just tell him the car is functioning fine. If he was really slick he could disconnect the light and tell you the problem was fixed that will we 500 bucks for refilling the headlight fluid.

Many local auto-parts stores will hook up the scan tool and read the codes for you for free. I know Auto-Zone does around here. Then you can get an idea of the cost and complexity of the repair.

Also, generally, the check engine light will begin to blink if the problem is bad enough to cause an imminent breakdown (high-temperature, low oli pressure, etc.).

I agree that the code reader will give you a code that will bitch about something. It is possible that something is just fine and the sensor has the problem. Some “Check Engine” lights stay on once they are tripped even if the problem was detected only temporarily and may not mean much. A mechanic can reset it and see if it comes back on again. You could try disconnecting a battery cable for a minute. That will sometimes reset the sensors without any cash outlay.

While knowing what the code is will point you in the correct direction, this information does not necessarily give you a clue as to what the cost of the repair will be. For example a code of P0102 could be tripped by an air leak caused by a hose that fell off (very cheap to fix) or a hole in the intake trunk ($20-75 to replace), a bad mass airflow sensor ($75-300 depending) or an electrical problem that will cost you $100/ hour to fix. Care to spin the wheel of fortune?

A flashing malfunction indicator light (MIL) or check engine light indicates a severe misfire that could result in damage to the catalytic converter. The engine management system does not care if the engine has oil pressure. It is designed to monitor for excess emissions. Low oil pressure does not cause excessive emissions (Yeah I know if the rings get worn out, but give me a break here)
Further more the system does not have precognition, it cannot predict when a probelem is imminent.

FYI - my check engine light will come on if my gas cap isn’t tightened down all the way.

I know Chevy and Chrysler do this… not sure about Hyundai, but it’s something to check.

Check your manual. Sometimes cars have predetermined service intervals, and the check engine light comes on for that reason. Some cars need special code readers, and the cost to get the code read can be relatively steep. My brother’s Catera needed such a check, turned out it was the mass airflow sensor, just the test cost him $150.

The car still has value. If you can find out what the cost of the repair is, consider just selling it as a fixer-upper with the problem included in the ad.

Good luck!

All cars after 1995 must be OBD-2 compatible. None of them should require a “special” code reader.

I don’t doubt that, it only makes sense. “All cars” makes me wonder though. Do you have a cite?

the cabbie solution for a constant or intermittent “check engine” light is electrical tape. just a small square or two should cover that bugger up real good.

also note; if you hear a faint clicking, rattling, or pinging sound coming from your engine, try turning up the volume on your radio. that won’t fix major problems, but it will keep the minor ones at bay for good.

We have a 1991 Safari van and the check engine light has been on intermittently since shortly after we bought it in 2000. It has been in for regular service and checked, and while it will go off for a day or even a month or two, it comes back on eventually.

True story: My check engine light has been on constantly for over four years. I took it to the dealer the first time, he mentioned the gas cap thing as a possibility, but could find nothing else. As the car was bought new, and I barely drive it, the odds of an actual problem at my mileage are low, so I have ignored it.

Do a search on “OBD-II” and there’s plenty of cites. I too thought it was 1995, but wiki says it was made mandatory for all cars produced in 1996 and after, so some late year 95s will have it as well.

If you check the essential fluids, engine oil, coolant, transmission fluid, and the car isn’t making any strange noises, the engine is running smoothly and you don’t detect any unusual smells (such as overheating might produce), it should be safe to drive, at least as far as the dealership to get it checked out.
Something as simple as a leaking vacuum hose will make the light stay on. I’ve driven cars w/ the idiot light on for months, as long as I frequently (weekly) checked the items listed above.

I just happen to have an OBD-II scanner and it’s book under my desk. From the beginning of the book

“Federal law requires that all 1996 and newer cars and light trucks sold in the United States must be OBD II compliant; this includes all Domestic, Asian and European vehicles.”

I have a Toyota and we’ve been told repeatedly that the problem after a few years is often the lights themselves. Nothing is wrong with the engine but some stuff connected to the warning llights has to be replaced. Of course, it’s tricky to know what to do when but I’d go with what A. R. Crane said if I needed to use my car before I could get it to the mechanic.

We bought a 2005 Hyundai Elantra; the sales person was at great pains to warn us about this.

OK, from the top. The following applies to cars sold in North America.
Some cars for the 1994 MY were OBD II compliant. A few more 1995 cars were OBD II compliant, and all cars 1996 and later are OBD II compliant. OBDII means that certain components are checked, and (same as OBD I) and readings are checked for plausibility (new for OBD II) In addition several new systems are monitored. For example, evaporative system, and catalytic converter operation.
What is plausibility? OBD I systems checked for short circuits, and open circuits to a sensor. OBD II check to see if the reading from the sensor makes sense. For example engine temp never rises above -20 after 10 minutes of driving? OBD II would set a code, OBD I would not.
To read the codes requires the use of some type of code reader. Unlike OBD I systems the codes cannot be read out using a paper clip, or pushing buttons on the climate control.
MIL lights do not come on at pre-determined intervals. They are not service reminder lights.
What are the most common reasons for MIL lights to come on? Probably the single largest reason is a loose or mis applied gas cap. OBD II systems check the integrity of the evaporative system, and if the gas cap is off or loose the system will fail that check. All OBD II systems are supposed to have a provision to turn off an intermittent MIL, but some of the early systems this feature was buggy and often hard to accomplish. After car makers got many cars shoved up their ass in buy backs from MIL lights, the systems got more friendly as to the drive required to turn off the light after an intermittent problem. What this means is that on some cars, a loose gas cap will light the light, and leave it lit until it is erased with a code reader.
Probably next most common would be some other problem with the evaporative system. Vacuum lines falling off, or split.
After that would come plausibility failures in various sensors. Every car has it own quirks, and the fixes vary for each.
After that the most common would be misfire diagnosis. Misfire is very damaging to the converter, and potentially the most expensive repair.

While checking the engine oil, coolant, and trans fluid is always a good idea, none of that is monitored by the Engine Control Module, and none of it would turn on a MIL.

For you guys that have had the lights on for a long time, how do you pass a smog test? :confused:

Wisconsin doesn’t have smog tests. The gas cap thing was brought up in our case too, but after every tank it comes on, and yes we do make sure the cap is on tight.

We’ve had that damn light on and off for 10 years. It’s really a pain in the ass. We’ve taken it in a hundred times. I think it’s the sensor or a haunted lightbulb. If they can’t find anything wrong, what are ya gonna do?