The 600 is indeed different. It uses the honda type system (s you have a red key with a chip in the keys for the immobiliser) and the fob only actually operates the central locking. I am 99% sure that you cannot add fobs as the system is seperate to the rest (the unit is part of the interior light) and so the only way is to get a replacement unit and new fobs together.
At the end of the day it is only remote locking so if it dont work properly just unlock with the key.
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