Electrical System: Immobilizer

System description 

The Immobilizer contains the Central Electronic Module, Engine Control Module (ECM), Driver Information Module and Immobilizer Antenna Unit.

The Immobilizer Antenna Unit is connected to the Central Electronic Module via two cables with serial communication one of which contains the immobilizer clock signal and the other contains the Immobilizer Data Signal.

Functionally the system is divided into two:

• Transponder check via Central Electronic Module, Immobilizer Antenna Unit and transponder.
• Immobilizer check with Central Electronic Module, Engine control module (ECM) and Driver Information module.

Both checks are activated when the ignition is switched on.

The transponder check is controlled by the Central Electronic Module. Central Electronic Module carries out a transponder check by communicating with the transponder via the Immobilizer Antenna Unit.

The immobilizer check also consists of a communication between the Central Electronic Module and Engine control module (ECM) to check the VIN and Immobilizer PIN codes in the units.

The VIN code is unique and is self programming in the engine control module (ECM).

It also includes the result from the transponder check. The communication occurs in the CAN high speed network.

If the checks are OK, the engine control module (ECM) permits the engine to start by sending an approval signal to the central electrical module which connects the starter relay to the starter motor.

Communication with the Driver Information Module only takes place if one or both the checks is not OK.

Transponder 

In the key there is a transponder which is a passive component. The same type of codes as in the S/V 70 are stored in the transponder (security code, key code or transponder ID). The security code is stored in VITAL (a new database replacing QW 90), while the key codes are only stored in the central electronic module. When replacing the central electrical module all the codes except the key codes are obtained in VITAL and programmed into the central electrical module, which then has the same codes as the old one. Because the key security code, stored in VITAL, is also programmed into the new Immobilizer in the central electrical module, the new central electrical module will recognize the keys as soon as the keys are programmed with the key codes. Each of the keys must be programmed into the central electrical module.

Immobilizer antenna unit 

The immobilizer antenna unit is located on and beside the ignition switch. (8097 C/R) There is communication between the immobilizer antenna unit and the central electrical module via two cables and antenna communication between the immobilizer antenna unit and the transponder.

The function of the immobilizer antenna unit is to modulate/demodulate (modify the carrier wave) and send/receive.

A digital code is received from the Central Electrical module which modulates the sending frequency and sends it to the transponder. The transponder replies by sending a distorted signal containing the key code, security code and the randomly selected code. These are demodulated and sent to the central electrical module.

ECM 

The engine control module (ECM) communicates with the central electrical module on the CAN high speed network.

When the ignition is switched on the engine control module (ECM) starts an immobilizer check.

The engine control module (ECM) transmits a calculated code to the central electronic module. The engine control module (ECM) receives/checks the central electronic module response code and transmits an approval to the central electronic module.

If the checks are approved the engine can start.

Central electronic module 

The central electrical module communicates with the engine control module (ECM) on the CAN high speed network, with the Immobilizer antenna unit via a two way serial communication and with the DIM on the low speed network. When the ignition is switched on the central electrical module starts a transponder check. The central electrical module calculates the awaited answer and compares it to the answer received from the transponder. The central electrical module only permits the engine control module (ECM) to start the engine if the calculated and received response are the same. The central electrical module and the engine control module (ECM) are recognized in an immobilizer check by exchanging calculated codes and comparing them. The central electrical module checks the engine control module (ECM) code and sends a reply which contains the information about the transponder check. If the immobilizer check is not OK, the central electrical module transmits a signal on the low speed network to the driver information module with information about the fault.

The immobilizer function (that the car cannot be started) is activated when the ignition is switched off and the key removed from the lock.

DIM 

The Driver information module communicates with the central electrical module on the CAN low speed network. When the ignition is switched and neither of the previously mentioned checks are approved the Driver information module receives information from the central electrical module and displays a diagnostic trouble code (DTC) on the combined instrument panel display.