Antitheft and Alarm Systems: Description and Operation

GENERAL DESCRIPTION

IMMOBILIZER SYSTEM
The immobilizer system consists of the ignition key, the key ring antenna, immobilizer-ECU, and the PCM. The ignition key has a built-in transponder. The key ring antenna is installed on the steering lock key cylinder. Only the registered ignition key permits the engine to start, therefore, the engine can never be started by means of a forged key or by connecting the ignition wiring directly. The system is significantly safe and reliable against theft. In addition, the driver has only to turn the ignition switch to the "ON" position to activate the immobilizer system. If the requirements for starting the engine are not satisfied, the engine will be immobilized. If a registered ignition key is lost, all your ignition keys need to be registered again using scan tool MB991958 (MUT-III Sub Assembly) to ensure security (Refer to Service and Repair/Procedures/How To register Encrypted Code). An additional ignition key can be registered as follows (only if no ignition keys are lost):
- Using scan tool MB991958 (MUT-III Sub Assembly) (Refer to Service and Repair/Procedures/How To register Encrypted Code).
- By operating two ignition keys that have been already registered (Refer to Service and Repair/Procedures/How To register Encrypted Code).

OPERATION
1. When the ignition switch is turned to "ON" position, the PCM sends a requirement for the encrypted code to the immobilizer-ECU (at this time, the engine is remobilized).
2. When the immobilizer-ECU receives the requirement from the PCM, the immobilizer-ECU supplies power to the transponder inside the ignition key via the antenna. The energized transponder sends the encrypted code back to the immobilizer-ECU via the antenna.
3. The immobilizer-ECU judges the encrypted code with its code logic in itself. If they are identical, the immobilizer-ECU sends the encrypted code to the PCM.




4. If the PCM can not receive the encrypted code, the engine will be immobilized.




CAUTION WHEN REPLACING IMMOBILIZER SYSTEM RELATED PARTS
To replace immobilizer system related parts, refer to the table given. When the ignition key is re-registered with scan tool MB991958, the originally registered ignition key registration information will be lost.