Although I have no specific knowledge on your perticular van, I'd suggest that the locking issue you have could be caused by the system thinking that one of the doors is not closed. This would be caused by a failure of one of the switches on each of the doors. This could be a press in plunger switch on the door frame, or a micro switch that is wired onto the door latch inside the door. With a van, I'd look around the sliding door first to see if there are any electrical contacts that are dirty. Eliminate any doors that currently activate the interior light correctly when opened and concentrate on the doors that don't.
Rupert
March 2020