Parking sensor reset
 

1996 S600
I got a bodyshop to change my front bumper.
When I got the car back, the parking sensors didn't work.
I took it back and got them to switch the sensors from the "new" bumper for those from the old bumper (which worked before I took the car in). Still didn't work.
I assumed they had over-stretched the cable or messed up the connector.
New local MB mechanic says he has the same trouble with his MB and has not yet found a solution, but he says the parking sensor system needs a reset after a disconnection.
Does anyone know how this is done?