After sitting for an extended period of time GXPsy had a dead battery. Quite dead. After replacing the battery the remote keyless entry and tpms did not respond. Both are controlled by the same module. After searching some databases I located a TSB about this very problem. TSB# 08-03-16-001b. It seems that if the car sits long enough the memory in the module disappears, only to need reprogramming to return it to operative. This impacts only the 2008 model year of a number of the GM product line. Of course, GM does not consider this to be a GM reponsibility and the cost to reprogram is borne by the customer. $110.00 later GXPsy once again has working keyfobs and TPMS.