Ok if its flashing the end light 4 times this is usually down to the door lock itself.
Its quite a common fault on the older models as ive replaced loads of them in the past.
What you need to do is open the door and remove the plastic clamp around the door seal.
Then unlip the door seal and peel it back.
Then remove the 2 screws holding the lock on and then pull the lock through the porthole.
Remove the plastic cover over the wiring and then inspect the wires as sometimes they can burn. If it has then the door lock will need to be replaced and the wiring retagged.
But if the wires are fine and the door is closing ok then its going to be the lock itself which you can just replace from there and that should cure the fault.
Now there is a slight chance it may be the control board. So if replacing the lock doesn't cure it then the control board will be the fault. But 8 times out of 10 its the lock itself at fault here.
If you need anymore info just get back to me.
No worries. If you need anymore info just get back to me.