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VW and Audi group (V.A.G) immo systems and how they work.

over the years v.a.g have been one of the leading companies in their security and today we will be explaining there different generations of immobiliser systems in detail from immo II to immo IV.


immo II - The Immobiliser authentication process begins with the car key and the ignition coil. when the Car Key is inserted into the ignition cylinder and rotated to the position just before starting, a signal is sent from the ignition coil that energises the electronic transponder in the key. The electronic transponder in the key responds to the ignition coil with a fixed code signal. The ignition coil on the ignition cylinder receives and forwards the signal to the immobiliser control module. if the fixed code signal sent by the key matches the code stored in the immobiliser control module, the variable code transmission starts. As soon as the immobiliser control module recognises the key, it generates a random number and sends it to the key. The car key and immobiliser control module then perform an algorithmic calculation, the cars key sends the result to the immobiliser control module. The immobiliser control module compares the number it calculated to the number calculated by the vehicle key. if the numbers match, the immobiliser control module sends a signal to the engine control module to start the engine. this is all completed instantaneously.


immo III - this immo system works very similar to immo II, but adds the engine control module to the algorithmic calculation process. Same as the previous immo system the process begins when the cars key is inserted into the ignition cylinder and rotated to the on position before starting. signals are exchanged, verifying the key is coded to the car. When the immobiliser control module recognises the key, it sends a random number to both the key and the engine control module. the car key, engine control module and immobiliser control module perform an algorithmic calculation on the number. the car key and engine control module send their results back to the immobiliser control module via the CAN data bus. The immobiliser control module compares the number it calculated by the cars key and engine control module. With this immo system all 3 numbers must match before the immobiliser control module sends the engine start signal the engine control module.


immo iv - As with the previous versions, immobiliser IV firsts verifies the cars key, then generates a random number. The random number is broadcast to the CAN bus and read by multiple components. these components perform algorithmic calculation on the number and the results are compared by the anti-theft control module (varies by model). If the results are the same, the anti-theft immobiliser control module broadcasts a message on the CAN bus, allowing the engine to start.


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