Ignition Key
There is a communication circuit in the ignition key, known as a transponder. This circuit is supplied with power from the magnetic field that is formed around the antenna ring when the central electronic module (CEM) activates the antenna ring. Consequently, the transponder is not dependent on a further power supply.
In order for the key to be used in the vehicle, a code in the key must be entered by the central electronic module (CEM). When the vehicle is delivered from the factory, two keys are normally programmed. When a key has been programmed for the central electronic module (CEM), the key is locked and cannot be programmed for another vehicle.
Scheme 2157
The engine control module (ECM) (4/46) controls the ignition system in the vehicle and controls activation of the starter motor via the starter motor relay (applicable to B8444S only). The engine control module (ECM) also grants permission to the central electronic module (CEM), indicating whether the fuel pump is permitted to run when ignition is attempted. These functions are activated once an approved check of the ignition key has been carried out and an identity check has been carried out between the engine control module (ECM) and the central electronic module (CEM) and the result approved.
In order for the engine control module (ECM) to work in the immobilizer system, the control module must be programmed with codes. This takes place for the first time during assembly in the factory, and subsequently takes place in the event the control module is replaced (when downloading software).