Electronic's , aren't they great ? There is a control module (power lift gate module ) Switch (sensor) inputs to the module . Lift gate obstacle detection strip right and left , liftgate cinching motor ,liftgate unlatch motor .Liftgate drive motor assemblys left and right . Probably a bad switch feeding bad voltage signal to the control module ! Like one of the obstacle detection sensors maybe. Could possibly have DTC'S - diagnostic trouble codes stored in the control module. Your best bet maybe to have the dealer run diagnostic's on it , check for codes . Need a factory or professional type diagnostic tool to do this. I would say you mite be able to check the sensor inputs to the module , don't know what or how much voltage > Some of these circuit's are a five volt signal from the module . Ohm check the obstacle detection sensor ? I still think best thing would have it checked for DTC'S . Almost forgot about the thing opening when you close another door , All the modules on the vehicle are connected on what is call a serial data network . Doors have modules inside as well .could be commanding that door open some how.
If you would like to see what your up against , here is a web site for free wiring diagrams
http://www.bbbind.com/free_tsb.html Enter vehicle info. year , make , model and engine size. Under system click on body & accessories , then under subsystem click on power liftgate. Click the search button ,then the blue link. The second diagram down starts liftgate diagrams . Good luck !
