Owner's Manual for the vehicle. With a quick reference ... - E38.org

Electronic vehicle immobilizer
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The key to security
Your BMW is equipped with a passive
anti–theft system. This electronic immobilization
system is designed to reduce
the susceptibility of your vehicle to theft
by making it impossible to start the engine
using any means other than the
special keys furnished with the vehicle.
Your BMW center can cancel the electronic
system authorization for individual
keys (for instance, in the event of
loss). A deactivated key can no longer
be used to start the engine.
How the electronics work
At the heart of this system is an electronic
chip which is integrated into the
key. The lock mechanism itself is actually
a dual-function device, simultaneously
serving as a communications
interface designed to allow the security
system to maintain a continuous stream
of variable, vehicle-specific signals with
the electronic circuitry in the key. The
system will not release the ignition, fuel
injection and starter unless it recognizes
an "authorized" key.
Force applied to the key can damage
the integrated electronic circuitry.
A damaged key can no longer be
used to start the engine.<
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