2. Immobilization
WARNING: This page is about a different car, the 2005 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.
When the ignition is switched on, the CIM checks that the correct key is inserted in the ignition switch. A circuit built into the remote control part of the key sends a code by means of inductance to a coil in the ISM. The code is passed on via a C-cable to the CIM, which checks that it is correct. The CIM also checks that the right MIU, BCM and PDM are fitted in the car. These are all part of the car's "immobilizer environment" and continuously send an ID number over the bus. If the key and control module ID numbers are OK, the CIM will send a message for "Immobilizer OFF" on the bus. The ECM acts on this information by cancelling fuel shut-off, which is always activated whenever the ignition is turned on.