Hi Pete,
If you have new fob you will need to visit Vauxhall, they need to use Tech 2 to synchronise the new fob.
If you are just replacing the battery, make sure you gently bend down the arm that goes to the top of the battery before fitting the new batt, these fobs suffer from poor connection.
Then simply switch on ignition and within 10 secs hold down the 'unlock' button, the central locking will cycle twice, and resync the fob.
This does not work if you have a fob from another vehicle.
Regards
Les Jones, April 2007
