I have a 2010 Yukon XL with the power lift gate. My power lift gate will not operate using either switch on the lift gate (outside handle or inside bottom of the door). It will, however, operate perfectly using the key fob or the switch located in the front console near the sunroof buttons. The problem started after a winter storm where the roads were really wet. Seems to me something may have shorted out inside the rear lift gate. Any suggestions on how to diagnose and fix this myself? Please let me know. Thanks!