Vito W639 central locking problem

[BohemiaMotors]

Hi, i have run ouf of ideas. My 2004 vito wont lock side doors and rear doors with remote key. The front doors work fine. When i try the button from inside only front and tailgate doors lock. No response from side doors. Any ideas what to try ? I can only lock them from inside manually by pushing down the knob.

 

[BIG UN]

Sliding side door contacts, you will need to either clean them or replace them.. you might be surprised as they aren't that expensive.. alternatively you can unscrew them from the body, check the wiring & clean the contacts and spray the connections with electrical cleaner