jaywalm

can anyone help my central locking is a bit hit and miss. i have changed the battery and the fob but sometimes it works sometimes not using the key manually it locks both doors but the fob when it works locks both doors but will only open the drivers i have rang a few auto electricians and they say go to dealers but would rather not with their prices just wondered if anyone knows a simple trick or test its a nissan 350z 55 plate. by the way my comma dosent work on here