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Immobilizer self-diagnosis - immobilizer III
General
Measures for eliminating current, model-specific faults => Technical Service Handbook Function The immobilizer III consists of the following:
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; Dash panel insert The immobilizer is a system designed to enable/disable the engine control unit (via CAN wire). The transponder code consists of a fixed code and a 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 warning lamp lights briefly (max. 3 s) and then goes out if an authorised vehicle key is being used. 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. The faults can be determined using the vehicle diagnostic, testing and information system VAS 5051 or the fault reader V.A.G 1551/V.A.G 1552. Note: The following description relates exclusively to the fault reader V.A.G 1551. Notes on use/matching of vehicle keys The engine will only start if use is made of an authorised key, i.e. of a key matched to the immobilizer. Vehicle key matching involves matching all vehicle keys, i.e. including spare and emergency keys, to the immobilizer. Matching must be performed for all vehicle keys if new or additional keys are required. If, for any reason, e.g. loss of keys en route, it is not possible to perform matching for all vehicle keys, customers are to be informed of the necessity of subsequent matching for all keys. It is particularly important to re-match all the remaining vehicle keys if any have been lost to ensure that the lost key is no longer authorised to start the vehicle. |
