A BMW with the EWS II system is sold with 4 keys, the keys are
each allocated a code, the code does NOT change.
There is a ring antenna around the ignition cylinder, and a transponder in the
key, when the ignition is turned on , the EWS control unit , via the
send / receive module under the steering column, sends a signal to the key, this
signal powers the transponder in the key and returns to the send
/ receive module with the keys code. If the code matches one of the programmed
codes in the EWS control unit, it will allow the starter to crank.
EWS II as of 97 now has a new input from the clutch pedal hall effect switch on
stick shift cars, this switch is the same one used for cruise
control, it now prevents the starter from engaging unless the clutch pedal is
engaged. This system is available only on the 97 E36 and E31
EWS III is now employed on all other models, it is similar but
amongst other minor changes , it no longer uses a send / receive module, it
access
the key directly from the EWS control unit. It is now also placed on a bus
system ( K bus) which allows for less wiring between the General Module,
Door Module , IKE ( instrument cluster ) and EWS III control modules.
Also, with the 97 model, the LED is back on the key of those cars fitted with FZV ( remote keyless entry )
EWS systems come with 4 keys, you should receive 4 keys when
you buy the car new, if not, the dealer has been instructed by BMW to replace
the EWS
control unit with a new one and 4 new keys. Reason for this is that the EWS
control unit has the facility for only 10 keys. If you buy the car new and
the dealer has lost 3 of the keys, you have 3 less that you can loose before the
expense of replacing the entire system.
Also, any individual key can be disabled, if your wife runs off with another guy
and takes a key to your pride and joy with her, a trip to the
dealer with the remaining keys will enable the tech to disable her key, so she
cannot start the car.
