When I lock my 4 yr old 406 HDI 90, the locks sound as if they are locking but immediately they unlock again. The dashboard display shows that no doors are open. I think the problem is in the front passenger door or the boot. If I play with the locks on these two, then the car will start locking OK again. Of course, since the key loses the sync with the car after a few attempts, I cannot keep trying this until the car does decide to lock! Can anyone shed any light on the problem. Thanks.