European owners (don't know about others) are aware that there is a switch in the trunk on the passenger side which can disable rear parking sensors. Switch is prone to accidental switching by luggage. This can be dangerous when backing off and expecting warning. Today I decided to solve it by shorting this switch. THIS IS A MISTAKE! Sensors work only when switch circuit is OPEN. So if you want like me to have always working sensors you simply have to disconnect the switch by means of disconnecting the little black plug 10cm below. (It's wrapped in insulation.)
