2010 Z71 electronic liftgate won't latch closed when using buttons. Door closed to bottom and then returns to open position. Have to close manually. Code reader show no codes. Perhaps some kind of sensor that is off? Have searched threads but have not seen anyone else with this problem. Any suggestions would be greatly appreciated

 

There are sensors in the liftgate. Need an advanced shop level scan tool to read those codes. P code scan tool will not read them, need a scan of all 4 code families to see what's going on as a first step.