Based from my experience :


Old the key is not functioning right?

And there is no way to re- sync the old key to the vehicle?

If both are true , then new key + key coding + vehicle sync
Otherwise old key can be used to initialize the sync with the new keys

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Build Date: 06/2004

2004 E53 3.0L 6 Cyl
Engine Code: M54
AT: 5L40-E/GM5 (A5S 390R)
http://s101.photobucket.com/user/lho...in/library/E53

2004 E46 M3 Coupe 3.2L 6 Cyl
Engine Code: S54
MT: S6S 420G - 6 speed
http://s101.photobucket.com/user/lho...in/library/E46
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Build Date: 10/2008
2009 E90N 328xi Sedan 6 Cyl
Engine code: N51
AT: GA6L45R/GM6
http://s101.photobucket.com/user/lho...in/library/E90