Antitheft and Alarm Systems: Description and Operation
Immobilizer SystemHow the Circuit Works
The immobilizer system is designed to prevent the car from being started without the owner's ignition key. If an attempt is made to start the car with any other key, the immobilizer system will disable the car's fuel supply.
The immobilizer system consists of the ignition key, immobilizer control unit-receiver, immobilizer system indicator, PGM-FI main relays, fuel pump and the ECM/PCM.
With the ignition switch in ON (II) or START (III), the immobilizer control unit-receiver and the ECM/PCM receive an "ignition on" signal through fuse 6 ('02-'04) (in the under-hood fuse/relay box) or fuse 32 ('05-'06) (in the under-dash fuse/relay box) and the PGM-FI main relay 1. The ECM/PCM then sends power to the ignition key transponder through the immobilizer control unit-receiver. The transponder then sends a coded signal back to the ECM/PCM through the receiver. If the signal is correct, the ECM/PCM will energize the car's fuel supply system by grounding the PGM-FI main relay 2. The immobilizer system indicator flashes a code to indicate that the correct key has been inserted. If the ignition key signal is not correct, the ECM/PCM will not energize the car's fuel supply system by not grounding the PGM-FI main relay 2. The immobilizer system indicator then flashes a code to indicate that an incorrect key has been inserted.