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Actions of the immobiliser at engine start-up
If an Audi A5 is started with the ignition key in the electronic ignition lock, the immobiliser runs several que-
ries and actions before the engine is started:
1 After a normally open contact is detected, the ignition key and convenience system control unit J393
exchange immobiliser data with one another. The convenience system control unit determines whether
the key is authorised for the vehicle.
2 The convenience system control unit now exchanges immobiliser data with the electrical steering column
lock control unit J764. If the device in question is the steering column lock adapted to this vehicle, the
convenience system control unit enables the steering column.
3 Terminal 15 is then connected by the convenience system control unit.
4 After "terminal 15" is connected, the convenience system control unit can communicate the engine and
the gearbox control unit. If these devices are also identified as control units which have been adapted to
this vehicle, starting of the engine is enabled.
Replacing immobiliser components
The process of replacing immobiliser components has been greatly simplified with respect to the subsequent
adaption procedure. The diagnostic tester routine recognises independently which component has been
replaced and adapts it or queries whether keys have to be adapted. In this way, it is possible to adapt compo-
nents of the immobiliser or even to install and adapt immobiliser components which were previously installed
in another vehicle.
After the loss of an adapted ignition key, there are two possible approaches:
1 readapt the remaining ignition keys - after that, the lost ignition key can no longer be used for starting the
vehicle (caution: of course, the key can still be used to open the vehicle via the lock in the driver's door).
2 replace the lock set and order a new set of ignition keys for the vehicle. This is the more expensive and
safer variant, the advantage being that the key's finder cannot open the vehicle. In this case, the vehicle
receives a new identity, i.e. it is no longer possible to readapt the lost (i.e. remaining) ignition key to the
vehicle.
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