Function

Function

Communication




When the system is activated communication occurs between the immobilizer control module and the engine control module (ECM) and between the immobilizer control module and the transponder in the ignition key.

Starting the engine
When an ignition key is inserted in the ignition switch the immobilizer control module transmits a code to the transponder, which responds with its own encrypted code. This code is decrypted in the immobilizer control module and is compared to the learned codes in the control module. Key validation takes a maximum of 300 ms. If the codes correspond the immobilizer control module begins communicating with the engine control module (ECM). This communication is encrypted and only permits communication between two units, the immobilizer control module and the engine control module (ECM), where the engine control module (ECM) continuously monitors the communication.
After the key has been validated and the engine started, a question-answer routine checks regularly that the key is still in place.
If the communication between the immobilizer control module and the engine control module (ECM) should stop while the car is driving, after cable breakage for example, the engine will continue to run. When the engine stops the engine control module (ECM) will go to the blocked position and the engine cannot be restarted.
If for some reason the engine should stall, due to incorrect gear selection uphill for example, communication is not re-established even if the ignition is switched on and off again within 4 minutes.

Stopping the engine
When the ignition is switched off, the immobilizer control module deactivates the functions in the engine control module (ECM) and the control voltage to the starter relay 3 seconds. Deactivation of the engine control module (ECM) occurs through the immobilizer control module transmitting a deactivate command three times.

Reinitiating
In the event of a voltage drop in the engine control module (ECM) the information about which mode the immobilizer control module was in may be lost. If this should happen, the engine control module (ECM) reinitiates communication with the immobilizer control module if the vehicle speed is below 30 km/h (19 mph). If the speed is above 30 km/h (19 mph), communication cannot be reinitiated because the engine control module (ECM) assumes that the immobilizer control module was active. This means that the engine control module (ECM) goes into blocked mode as soon as the ignition is switched off.

Disarming the alarm
When the ignition is switched on the immobilizer control module checks that a valid key is in the ignition switch. If there is a valid key in the ignition switch the immobilizer control module transmits a code to the VGLA (Volvo guard lock and alarm system) control module. If the code is correct the VGLA (Volvo guard lock and alarm system) control module will deactivate the alarm.