Immobilizer Description and Operation

Immobilizer Description and Operation

The immobilizer system functions are provided by the theft deterrent key transponder. When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the transponder embedded in the head of the key is energized by the theft deterrent key transponder amplifier. The energized transponder transmits a signal that contains a unique value, they key code signal, which is received by the theft deterrent key transponder. The theft deterrent key transponder then compares this value to a value stored in memory. If the value is correct, the theft deterrent key transponder sends a communication ID to the ECM. If the ECM determines this ID is valid, engine starting will occur. The components of the immobilizer system are as follows:

* Engine Control Module (ECM)
* Theft deterrent key transponder
* Theft deterrent key transponder amplifier
* Ignition key alarm switch
* Vehicle keys

Theft Deterrent Key Transponder

When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the transponder embedded in the head of the key is energized by the theft deterrent key transponder amplifier. The energized transponder transmits a signal that contains a unique value, they key code signal, which is received by the theft deterrent key transponder. The theft deterrent key transponder then compares this value to a value stored in memory.

The theft deterrent key transponder communicates with the theft deterrent key transponder amplifier. Vehicle the vehicle keys are energized, the theft deterrent key transponder amplifier receives the key code information and passes them to the theft deterrent key transponder, where they are compared to the stored value.

Engine Control Module (ECM)

The engine control module (ECM) verifies that the communication ID received from the theft deterrent key transponder is correct. The ECM can learn only one communication ID. If the communication ID is correct, the ECM enables the starting and fuel delivery systems.

Theft Deterrent Key Transponder Amplifier

The theft deterrent key transponder amplifier contains a section of coiled wire that surround the ignition cylinder. This coil acts as an exciter and passively powers the transponder located in the vehicle key when it is placed in the ignition cylinder. With the vehicle keys passively powered, the key code is passed from the vehicle key to the theft deterrent key transponder amplifier, which acts as an antenna. The key code is then set to the theft deterrent key transponder.

Vehicle Keys

The vehicle keys contain an unpowered transponder which holds a unique key code. When the key is placed in the ignition cylinder, the transponder is passively powered and the key code is broadcast.

Ignition Key Alarm Switch

The ignition key alarm switch is a normally open switch which closes when a key is inserted into the ignition cylinder. The theft deterrent key transponder monitors the ignition key alarm switch signal circuit and when a key is inserted into the ignition cylinder, the theft deterrent key transponder will begin the immobilizer sequence by activating the theft deterrent key transponder amplifier and begin looking for the vehicle key to transmit a key code.