System Operation

• When the ignition is switched on (7)  and an attempt made to start the engine the E.C.M sends an unlock request (8) to the immobilizer control module. (2)
• The immobilizer control module outputs a 100-150 kHz carrier wave (9) to the antenna ring. The signal is induced into the transponder (10). The transponder responds to this induced signal by outputting the key code identification (11) witch is transmitted back to the immobilizer control module (12) via the antenna ring.
• This key code identification is then compared with the stored code in the immobilizer control module memory. At this point the immobilizer control module only recognizes this as one of series of registered keys.
• To further increase security, the immobilizer control module transmit a random code to the E.C.M (14) and the key transponder (13) and request an algorithmic calculation to be performed. the immobilizer control module also performs this algorithmic calculation independently.
• The E.C.M  and key transponder return the answers of the algorithmic calculation to the immobilizer control module (15)&(16). A comparison is made and if they match, the unlock request (17) is granted.
• If any of the calculations do not match the unlock request is denied. the engine will not start or, if already started, will stop.
• This authentication procedure happens so quickly that the driver may only be aware of a very slight delay between the key being turned and the engine starting.
• The immobilizer system is automatically reset when the ignition is switched off and the key withdraw from the ignition switch.
• Many immobilizer systems feature fault memories which can be accessed in various ways by counting immobilizer warning light flashes, bridging data link connector (D.L.C) terminals with a voltmeter or LED tester, or using suitable diagnostic equipment.