I just scanned my boss's L36 Bonneville this weekend for a similar thing. Car ran perfectly, but the SES light came on. I hooked up the laptop and it showed P0128 I believe was Coolant Thermostat. Basically it didnt warm up enough. He said he would get a new thermostat and an coolant temp. sensor and bring it back by so I could replace them for him.
Sorry for all of your trouble. I know what its like to want to get the needed information and have to wait because of things beyond your control. Good luck with finding out what it is, hopefully something really simple.
