I have an 05 Corolla, and a few weeks ago the check engine light came on. I checked the oil and realized it was low, so I filled it up. Light stayed on. I figured it just needed some time for the sensor to catch up, so I didn't worry. A few days later the light was still on, so I took it to Advance since they do a scan for free. Their scan found no errors, even with the engine on. Any idea what this could be, or how to resolve it so that I don't potentially end up ignoring an actual problem?