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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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Old 10-03-2012, 04:03 PM
mej16489 mej16489 is offline
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Mein Auto: 07 X3, 03 525i, 04 986SE
2003 E39 Diamond Key Charging

Sorry, long post, but I know all the gorey details matter...

I've read through every key thread that I can get my hands on and I still have a question.

Is the mechanism for reading the transponder in the key the same mechanism which recharges the battery in the key?

I'm fairly certain that my wife's car is no longer charging keys and I would like to fix it.

As I understand it, near field rf radiation is used to 'activate' the transponder in the key when inserted into the ignition and turned to the start position. The car 'reads' the response and determines if its allowed to start the car. Essentially RFID...

Similarly, while the key is in the ignition with the car running, they battery in the key is recharged via inductive coupling (like a cordless rechargeable toothbrush).

Is it possible to have one of these functions work and not the other?

I have 3 keys. The 2 original full access diamond remote keys and 1 additional full access diamond remote key ordered from the dealer roughly a year ago. The Valet Key and I *think* maybe a plastic key were lost years ago in a move.

Pretty much only 1 key was ever used. The 'spare' key was put away with other spare keys in-case of emergency and likely never used a single day in its lifetime. So, when the remote in the 'daily' key quit working the spare was dead too. But of course both keys worked perfectly fine manually in the locks and to start the car.

Basically both of the original keys had reached their end of life on the remote batteries (so I assumed) so I simply ordered a new one.

Now, the 'new' key from a year ago has quit working to remotely lock/unlock.

The fuel door properly locks/unlocks when any of the keys are used manually in the driver's door.

Since the uncharged 'shelf life' of a key is rumored to be about 18 months, I'm guessing that maybe my wife's car is simply not charging keys...

Could something be misaligned with lock/ring antenna such that the keys start the car but not charge the keys?

I've monitored the keys with a spectrum analyzer and I'm not getting any RF out of all 3. So since the remote buttons are apparently doing nothing, I have not attempted to re-pair the keys.

Any advice?
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