I think the return signal is a power, if it is going to ground, the supply in car may be losing volts, so you could lose all sorts of Crap ( door open limit, door close limit, CAN going haywire) ctrl-alt-1 to open the picture of the door with limits and SE visible and see what happens when SE is blocked might help. If you are familiar with how to create log files, you may find an answer there too.