Can the rear defrost in a 2009 Impala be set to stay in the on position so it will activate automatically when the vehicle is started?

Yes it's possible but would be a custom electrical job for a professional. They use a great deal of amperage and that's why they shut themselves off when the engine is not running , the battery would go dead very quickly

Thank you for the response. Would this require an additional interface for a remote car starter that could be added post installation?

Ya got me on that one. Maybe somebody will know

Yes it could be added. It would be wired into the ignition power wire coming out of the remote start using a diode and a relay. You hit the remote start, the car starts, there will be an ignition wire that stays hot and once the remote start timer runs out the power will be removed from that wire. That wire will have to be cut and a diode put in so electricity can't back feed to the remote start box and then splice the relay in between the diode and the remote start box. Without the diode the rear defrosters will be stuck on every time you turn the key on because power will back feed into the remote start wire and trigger the relay. Like david said, yes and also like david said, have a pro do it. If someone says its not possible print this page out and take it to them. Anyone who is well versed in electrical will completely understand what I have written and be fully capable of carrying it out.

Thank you John. Don't worry, these are not things I even attempt. When it comes to vehicles I always go to someone who knows what they are doing. Just trying to narrow down the possibilities. One more question. The starter I have has different options for each button. For instance if you push the button and release it one event will occur but if you press and hold another event will occur. Would one of these buttons work for both starting the vehicle and activating the defrost?

Its quite possible but I'm not certain as to how yours is setup. Some are set up so you can add features like opening an electronic trunk release. If you were to figure out which wire on the box became active with that button, yes you could but it would have to stay "hot". If you tap into one that is similar to the trunk release wire then the rear defrosters would turn on for only a few seconds. If you know the make and model of your alarm you should easily be able to find all the info you need online regarding features. Let's say one of those button combinations turned on headlights, doubtful but just an example, the wire that feeds power for that would be perfect. Getting back to the other set up after thinking about it you could just tap directly into the defroster relay that is already there as long as you put a diode into the wire going to the defroster relay. If only you would have gotten the 09 with the factory installed remote start.