89 The coded ignition key

The engine immobilizer system is a theft deterrent system that is designed to prevent the engine of the vehicle from being started by any other means than the uniquely coded ignition key. The principal parts of a system are shown in Fig. 8.22.

The transponder chip in the handle of the ignition key is an integrated circuit that is programmed to communicate with the antenna (transponder key coil) that surrounds the barrel of the steering lock. When electromagnetic communication is established between the chip in the key and the transponder key coil, the immobilizer section of the ECM recognizes the key code signal that is produced and this effectively 'unlocks' the immobilizer section so that starting can proceed. Vehicle owners are provided with a back-up key that can be used to reset the system should a key be lost.

Transponder Chip

TrancnnnHpr Key Coil

Igniti'

Transponder Chip

Igniti'

Transponder Key Amplifier

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