Berlingo deisel 05 tailgate wont central lock/un ?

try this, take the cover off back door to expose the lock, spray WD40 over the moving parts, if this does not cure the problem, you might need to replace the lock motor. you can get one very cheaply from a scrapyard, and as they are easy to fit, i am sure you could get someone there to replace it for you.

hope it helps
November 2010