what is the most comman problem for a check engine light to come on in a toyota avalon 2011?

1st ones i have seen would be #1 o2 sensor if right maintenance schedule followed

Obd=On board diagnostic, you can buy one on line, they are very unexpensive nowadays, plug it in, get the code then google it, once you get use to it, it gets easier & you'll love it..

Or just pull into any Autozone or similar national auto parts chain store and they'll read it for you. Some even print out a report detailing the meaning of the code(s) read and common solutions.

Had same problem. Farmboy on CarGurus said to turn the gas cap until it snaps, then disconnect the battery for 30 seconds , then reconnect; problem solved. Strange but true.