General information: Function: Notes

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 Audi S8, 2003 Audi A8, 2002 Audi S8, 2002 Audi A8, and 2001 Audi S8. However, it is still accessible from the selected car via links, so may be relevant.

Immobilizer III consists of:

an adapted control module for anti-theft immobilizer (integrated in instrument cluster)
a warning light in instrument cluster
an induction coil at ignition lock
an adapted Engine Control Module (ECM)
and adapted ignition keys with electronics (transponder).

The control module for anti-theft immobilizer is integrated in the instrument cluster, e.g. if control module is malfunctioning, instrument cluster must be replaced. See INSTRUMENT CLUSTER, REMOVING AND INSTALLING .

The anti-theft immobilizer is a system for enabling/locking the Engine Control Module (ECM) via the CAN wire.

The transponder code consists of a fixed code and a variable code. This is different for every start procedure and therefore acts as a copy protection for the transponder.

Every immobilizer contains a different computational rule for the variable code that remains the same for its entire service life. During adaptation of the vehicle key, the immobilizer writes this computational rule into the transponder and simultaneously learns the fixed code of the current key.

The fixed code identifies each individual key so that a key that is lost can be blocked from usage. Each time the ignition is switched on, the induction coil for immobilizer reads the transponder's fixed code and then the variable code and determines whether this key is authorized for vehicle start.

The warning lamp lights up briefly (max. 3 seconds) and then goes out when an authorized vehicle key is used.

When an unauthorized vehicle key is used or when a system malfunction occurs, the warning lamp blinks constantly during ignition "on".

The electronic anti-theft immobilizer is capable of extensive On Board Diagnostic (OBD). If malfunctions occur in any of the system components, corresponding Diagnostic Trouble Codes (DTC) are stored in the DTC memory of the anti-theft immobilizer. Malfunctions can be determined via the VAG 1551 scan tool or VAS 5051 tester.

NOTE: The following description refers only to the VAG 1551 tester.