The first and most obvious thing to check is your key fob battery.
My fuel door wont lock on my 2007 audi a4.
If the plunger does not snap into locking position this component is damaged and needs to be.
I had a door on my 2007 b7 a4 which didn t lock.
This article applies to the audi a4 b7 b8 2005 2015.
Are you having problems.
As the door latched cables wires seemed fine.
With the fuel door open as the image displays press the plunger down to lock into position.
As you push it in you can feel the gears turning.
If a fresh battery fixes the problem consider yourself lucky.
My diagnosis was the door control module.
Window sometimes didn t work.
Audi a4 b7 b8 door lock problems diagnostic guide door lock problems diagnostic guide experiencing problems un locking your doors.
Door lock problems diagnostic guide.
If not also check your battery s voltage to make sure it s reading 12 volts with the ignition off and 14 volts with the ignition on and the alternator running.
Another bug bear are the wires inside socket in the door between the pillar door.
On the side of the gas door remove the panel from the trunk to locate the electrical harness.
Covering the diagnosis and repair of a faulty lock module on my b8 a4 avant 2008 these lock modules are used in several vag models which probably all suffe.
Make sure the electrical harness is connected.
Central locking didn t flash lights.
You can push it in with your finger but it takes force.
Check the battery of the fob try to lock and unlock the door from varying distances.
Changed door control module via ebay all ok now.
If you notice that despite being not terribly far away from the car it is not reacting to the queue to lock unlock the vehicle then it might be time to replace the fob battery.