Here in Texas we saw 'em off.

{Gig 'em.}

http://freediag.sourceforge.net/

You can always get a cheap OBDII interface from somewhere like Multiplex-Engineering and write your own. Or Scantool.net... or any other number of sub-$100 sources. Even Alex's tools at OBD-2.com are good enough. No need to reinvent the wheel though.

Once you start talking about hacking in to your PCM and changing things though, that's a whole other can of worms. People hold the keys to the kingdom on those VERY tightly.

They had a product called the SuperStat. It was a Honeywell programmable thermostat with an RF receiver module inside it. When the utility called for load control, they'd send out a paging signal and the thermostat would kick the A/C off for the amount of time contained in the message.

S-A also had gray boxes that went outside the house for A/C control, and they also worked with water heater and pool pump control. This is nothing new.

Call it "generating negawatts". Instead of positive megawatt generation, we're generating negative megawatts to shave peak. Yes, I worked with these things, and yes, I work for a utility.