Pull the codes from the computer, match the code to the troubleshooting procedure, follow the procedure to find the source. Repair the source, light will go out if that was the only problem. There are "monitors" or self test the computer runs the car through, if a problem occurs, it may not run all of the self tests until that problem is taken care. Therefore, another problem may exist. It is emission related. If you are unable to do this, take it to an independent repair shop and have them do it for you. We just called our mechanic yesterday about the same problem. He said that since he had just installed a new belt, the problem might be that we didn't screw the gas cap on tightly. After fixing the problem it could take 200 miles before the light goes off.
The 2014 Toyota Avalon has a V6 engine.
The 2012 Toyota Avalon has a V6 engine.
The 2005 Toyota Avalon has a V6 engine.
The 2008 Toyota Avalon has a V6 engine.
The 2003 Toyota Avalon has a V6 engine.
The 2009 Toyota Avalon has a V6 engine.
The 2004 Toyota Avalon has a V6 engine.
The 2001 Toyota Avalon has a V6 engine.
The 2013 Toyota Avalon has a V6 engine.
The 2010 Toyota Avalon has a V6 engine.
The 2011 Toyota Avalon has a V6 engine.
The 2006 Toyota Avalon has a V6 engine.