Astra G
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Function When the ignition is switched on, the immobiliser control unit requests the fixed code (transponder code) from the key [1.1] 1) and checks it [2.1]. If the fixed code is valid, the immobiliser control unit deactivates the anti-theft warning system if it is active at the time. The immobiliser control unit also cancels the interruption of the starter circuit via an external relay (optional, for the Netherlands only). At the same time as the immobiliser control unit requests the fixed code from the key, the engine control unit calculates a random number [1.2]. The engine control unit sends a request signal to the immobiliser control unit, signalling its readiness to communicate with the immobiliser control unit [3]. The random number is then requested by the immobiliser control unit [4] and sent from there to the transponder [5]. The transponder takes the random number (a programmed secret number and a constant) and uses a defined calculation procedure (cryptological algorithm) to calculate the alternating code [6.1]. The engine control unit independently calculates the alternating code using the cryptological algorithm at the same time as the transponder [6.2]. The alternating code calculated by the transponder is then sent to the immobiliser control unit [7] and is transferred to the engine control unit [8]. The engine control unit compares the two independently calculated alternating codes and, if they match, allows the engine functions to be activated [9]. 1) The digits in brackets refer to the function diagram in section 2.18.3.
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