2003 Elantra - Malfunction Indicator Light

Have the code read. Could be a bad sensor, could be a bag CAT converter. Some auto parts stores will read codes for free hoping you buy a part from them.

The MIL is frequently caused by the gas cap not sealing properly. This has not happened on my Elantra but when I had the Prizm it happened several times.

---MIKE---

This morning the MIL light turned off. If it stays off does that suggest the problem has resolved itself?

Yes, especially if it was the gas cap. After some number of drive cycles, it will reset and stay off. Assuming, of course, you put the cap on properly this fill up. Do not top off the tank either as it can cause the problem.

Regarding reading the code if/when the light is on, is it specific? In other words would it point directly at a poorly sealing gas cap as a cause?

It'll tell you the type of the problem the computer saw. In the case of a loose gas cap, it should report some type of fuel vapor leak. Once you know the type of problem, it's then time to see why it's occurring.

Great and thanks to everyone for responding. It does seem to be related to fueling since the light came on again after I filled the talk.

OK, easy to fix. Don't overfill, be sure cap clicks three or four times when you close it, or, since it is 9 years old, get a new cap.

On my Buick, I'd stop for gas on the way home and then drive 1.5 miles to my house. Next morning, I'd drive 1.5 miles again and the light would come on. I stopped filling to the very top and problem went away.