There was a problem with the older smarts where the solenoid that locked the
fuel cap closed would seize making it impossible to fill with fuel. Should you find
you are in this situation you have a few choices.
Knocking It Free
Sometimes a few knocks on the white plastic solenoid can free it allowing it to move.
Using a 10mm socket, remove the rear light on the same side as the filler cap,
removing the light can be seen here.
Tap it a few times while trying the unlock botton on your key, this should
eventually free up the mechanism to allow it to move properly.
I'm Low On Fuel With No Tools
You are only left with a single option, pull the cap open with all your might,
it will break the plastic catch on the inside of the cap. The cap can be replaced
at a later date when a new one has been purchased.
If you are lucky enough to have some torx bits, you can remove the filler cap cover by removing all of the torx bolts around the outside. One of the bolts is a dummy and doesn't need to be removed.
Replacing The Solenoid
Remove the inside boot panel on the same side as the filler cap, see here.
You will see a pair of torx bolts (circled red), remove these bolts.
Remove the rear light cluster on the same side, see here.
Reach in and lift the solenoid up, this unhooks the tab shown above (circled in blue).
Disconnect the electrical connection and pull the unit from the car.
Open the fuel filler cap before putting the new one in place.
The old solenoid is attached to a brass coloured plate, remove the bolts from the back
of this plate and remove the old solenoid. Refit the new solenoid to the plate,
reconnect the electrical connection and offer it back into the car,
Line the plate up and slot the hook (circled blue) back into position. Refit the torx bolts.
Test the solenoid works ok by locking and unlocking the car a few times. Close the fuel
filler cap and try locking it again to make sure it fastens the filler door closed.
Refit the rear light cluster and the internal side boot panel. Job done.
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