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◆ -> With immobilizer II (variable code), the keys are marked with a "W".
5.2 - General information
Function
The electronic immobilizer consists of the following:
◆ Immobilizer control unit
◆ Fault lamp in dash panel insert
◆ Reader coil at ignition lock and
◆ Matched ignition keys with electronics (transponder / response reader memory)
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 W-wire).
The transponder code consists of a fixed code (as with old system) 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 authorised for starting.
The fault lamp lights briefly (max. 3 seconds) and then goes out if use is being made of an authorised vehicle
key.
The fault 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.
Immobilizer self-diagnosis can now only be implemented using the vehicle diagnostic, testing and information
system VAS 5051
For security reasons, the immobilizer PIN is encoded. The encoded number (PIN = Personal Identification
Number) is made up of 7 digits.
The PIN can only be used with the vehicle diagnostic, testing and information system VAS 5051 as of basic
CD version V02.00.
The 7-digit PIN must be obtained by way of the appropriate Regional Sales Centre/importer on the basis of the
14-position immobilizer/engine control unit identification number.
The 14-position immobilizer/engine control unit identification number can be read out with the self-diagnosis
function.
The PIN is only valid for one day, after which a new number has to be requested. The PIN is of no use to the
customer or other dealerships.
Audi A3 1997 ➤
Electrical system Self-diagnosis - Edition 02.2002
5.1 - Immobilizer self-diagnosis - immobilizer II (variable code) 139
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