How do I get the check engine light on my 2006 Toyota Avalon to go off? A loose gas cap was the culprit

Hello Tom:

You can reset the check engine light by clearing the DTC code(s) at the ECM port using a code reader; or by disconnecting the ground (negative) battery cable from the terminal post of the battery- wait 5 minutes, then, press on the brake pedal or turn on the headlights to draw any remaining (residual) voltage current out of the electrical system.

Replace the ground cable to the battery...restart the car.

Should the check engine light come back on, the problem was not just with the gas cap, you will have to use the code reader to pull the trouble codes...and based on the code(s), you will then have to perform diagnostic troubleshooting to trace and locate the component part(s) that are triggering the events. If you suspect a particular part or several parts, you will have to test them at the component level to see if it or they are operating properly or are malfunctioning.

A lot of times if you disconnect the battery for couple minutes then hook it back up it will clear your computer and the light will go off. You will have to reset the radio after.