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permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.
-> In the new immobilizer III, as in the immobilizer II (variable code immobilizer), the keys are embossed with
a "W", indicating that the code is made up of a fixed portion and a variable portion.
Measures for eliminating current, model-specific faults
=> Technical Service Handbook
Function
Immobilizer III comprises:
◆ Adapted immobilizer control unit (integrated into dash panel insert)
◆ Warning lamp in dash panel insert
◆ Reader coil at ignition lock and
◆ Adapted engine control unit and
◆ Matched ignition keys with electronics (transponder)
The electronic immobilizer control unit is an integral part of the dash panel insert, i.e. the dash panel insert has
to be replaced in the event of a defective control unit.
=> Electrical System; Repair Group 90
The immobilizer is a system designed to enable/disable the engine control unit (via CAN wire).
The transponder code consists of a fixed code (as immobilizer I) and an additional variable code. This changes
whenever the vehicle is started and thus prevents the transponder being copied.
Each immobilizer has a different arithmetic rule for the variable code, which remains the same over the entire
service life. On vehicle key matching, the immobilizer writes this arithmetic rule into the key transponder and
at the same time learns the respective transponder fixed code.
The fixed code identifies each individual key, thus enabling a lost key to be disabled. Whenever the ignition is
switched on, the immobilizer reader coil reads out the fixed transponder code for the key and then the variable
code and checks whether this key is authorized for starting.
The warning lamp lights briefly (max. 3 seconds) and then goes out if use is being made of an authorized vehicle
key.
The warning lamp flashes continuously when the ignition is switched on if an unauthorised vehicle key is used
or in the event of a system fault.
The electronic immobilizer is provided with comprehensive self-diagnosis. Fault codes are stored in the fault
memory of the immobilizer if faults occur in system components. Faults can be determined using the vehicle
diagnostic, testing and information system VAS 5051.
Audi A8 1994 ➤
Electrical system Self-diagnosis 02.99 ➤ - Edition 05.2002
2.2 - General information 73
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