Cliff notes about remote keys:
The remote keys have 3 features/systems that are ALL independent of one another but work in conjunction with each other:
- EWS (immobilizer)
- FZV (remote central locking)
- DWA (anti-theft alarm siren system)
EWS shuts down starting/ignition/fuel and uses a transponder inside the key that communicates with the EWS control module and DME/ECU. If the ISN (individual serial number) that was assigned to your car's EWS components as it came off the assembly line don't communicate with each other...the car won't start. The only way to communicate with the EWS system is with dedicated hardware/software...and the ISN can NOT be changed. The transponder's ISN (and individual key codes 1-10) are already written to your EWS control module...thus there is no "coding" that is required for a new key to start your car if you purchase a new key (any key...even the non-remote keys) from a BMW dealership. A DEAD key battery will NOT affect the key's ability to start the car....EWS is self powered thru induction (ring antenna around the ignition & induction coil inside key powers up the EWS chip inside the key which allows it to send & receive data).
FZV is the central locking system, and the remote key transmits a one-way signal to the antenna in the rear window which is then sent to a receiver located in the rear top center of the vehicle which then sends a signal to the GM to lock/unlock the doors & fuel filler flap.
DWA is the anti-theft alarm siren system, and the remote key transmits a one-way signal to the antenna in the rear window which is then sent to a receiver located in the rear top center of the vehicle which then sends a signal to the GM to arm/disarm the alarm siren.
FZV & DWA require the use of the battery inside the key to send it's signal to the car. These 2 systems also can be programmed to other BMWs that have the same set-up (and radio frequency) to lock/unlock & arm/disarm the car. This is the procedure that can be done in your drive-way to reinitialize the keys to your car (by inserting key in ignition, removing, then pressing the buttons).
The EWS transponder can't be "recoded" to another BMW...it can get out of sync...and BMW DIS/GT-1 (and some of the aftermarket software) can
"resync" the EWS code tables...this can only be done with keys that have already been coded to your EWS control module (again, which have already been prepped for your vehicle when it rolled off the assembly line)...unlike the FZV/DWA features whereby any key that has the same frequency (315 MHz in the USA/Canada/Australia or 433 MHz in Europe) can be programmed to your vehicle.