I have a problem that my “check filler cap” lighter is always on, even if I take out my key and lock the car.
has anybody had a similar fault or a solutions?

the car is a Mini Cooper S r53 2002-model with stock navigation.

 

Your gas cap seal is probably cracked and leaking. Do a search for my cheap fix by using an off-the-shelf O-ring to replace the OEM seal. Mine has been working for nearly 10 years now.

Eric