Key Remote Fob Replacement

[cj10jeeper]

So where did I go wrong or what did I miss? I was being kinda smart and when my X5 key stopped opening the door I got a spare key off ebay having nearly died when BM wanted £62 per half hour to check the key then £100 for the replacement. Inc tax I was looking at a good £200.

Dissected the spare and got the electornics.
Opened my old key and pulled out the electronics
Dropped the spare electronics in the old key - so now I have correct blade an new internals
Ran a programming routine and it would open an close doors, set alarm however it would not start the engine.

Is there therefore some sort of transponder linked to the specific original key electronic module?

Actually it's really just curiosity as I found the fault on my old keys electronics and with a bit of deft soldering managed to fit a new microswitch in it from the spare..and believe me it is small

Rebuilt and the job is done and works perfectly....