e34 OBC lock

On my e34 if I set the lock on the computer nothing seems to happen and I am allowed to start the engine without entering the code I put in the lock.
I have had a previous e34 and e32 with this system and they worked fine with the OBC locking the ignition and sounding an alarm if you attempted to start without entering the code.
At some point I suspect the car had a factory alarm on it which has been removed, could the OBC lock funtion have been disabled somehow?
Steve Parry
K100RS SE & F650
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