ford sierra immobiliser

the immobiliser on my ford sierras kicked in and i cant drive the car.I have tried locking and unlocking the door and had the door panels off checking the
little catch thing that activates the immobiliser and its all fine.i only want to be able to drive it for a few more weeks so dont want it to be a big job. any ideas before a garage rip me off?please help me.thankyou.
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