The ECON button allows you to manually override the Autostop feature when you want to keep the AC in your car running at a stoplight. That is, if the ECON light is on, your car's engine will shut off when you stop. If the light is off, and you have the AC on, your car will stay running.

Notice that when you turn off your AC, the ECON light turns off as well. This is because your car will ALWAYS perform an Autostop if you're not running the AC; it has no other reason to keep the engine on. So the only function of the ECON is to keep the car powering your AC when it's so hot and sunny out that you can't bear to sit in the heat for a while at a stop.

If the ECON mode is on, and you have your fan set at a speed other than AUTO, you'll notice the air coming out of your vents suddenly go warm - the engine (and thus the AC compressor) has stopped, but the fans are still blowing. If the fan speed is set on AUTO, the vents will stop blowing air of any temperature. When it's really hot (this happens every day in SC now), I like to let my AC shut off at a stoplight but keep the fans running, providing at least a little heat relief until my AC starts up again at the green light.

Hope this helps, and enjoy your new car! I just got mine two weeks ago, and I'm definitely still in the honeymoon phase.