The purpose of the immobilizer system is to provide additional theft deterrence to the vehicle in which it is installed and to prevent it from being stolen or driven by unauthorized users.

The verification of the user authorization is done by an ignition key with integrated transponder.

The external LED displays the immobilizer status and has an additional theft deterrence function.

To secure the communication, the status is exchanged between the immobilizer and the electronic control module (ECM) in 5 bytes of encoded data. These 5 bytes are composed by a mixture of random data and two types of fixed code, a vehicle model identification number : MIN and a vehicle specific identification : VIN

The MIN is known from the first supply of the system.

The VIN is realized by immobilizer control unit (ICU) on the special order from the key coding (reading of transponder code and storing it as valid key code in immobilizer EEPROM).

A different random data is computed at each key transition.

All the immobilization communication between the ECM and ICU is made on K-line (K-line : Serial data line [rsquor]7’). Due to the learning of the vehicle specific identification number, both ICU and ECM can stay in 3 stable modes Virgin mode (VIN not learnt) Learnt mode (VIN learnt)

Neutral mode (for a new VIN learning)--In case of using valid key, the release message communication with the ECM takes place and the LED displays the immobilizer status valid key. In case of using invalid key, the ECM disables the fuel injector circuit with coded intervention and sets the DTC. The above conditions are maintained until the ignition is switched off.

An ECM without an immobilizer control unit cannot be interchanged for an ECM that is used with an immobilizer control unit system. The ICU and ECM must have a matching ID code. ID coding and key coding are accomplished by using Scanner-100. The immobilizer system consists of a maximum or 5 ignition keys with integrated transponder , the toroidal coil (Detection coil) for energizing and reading the transponder mounted at the ignition lock and the ICU.

The external status LED for displaying the immobilizer status

Each valid ignition key has an internal transponder which is a read/write transponder.

The transponder contains an implementation of a crypto-algorithm with 96 bits of user configurable secret-key contained in EEPROM and transmits data to the immobilizer control unit (ICU) by modulating the amplitude of the electromagnetic field, and receives data and commands in a similar way.

The toroidal coil is mounted at the ignition lock in front of the key barrel. It is connected to the immobilizer control unit (ICU) with a four terminal connector fixed at the body of the coil. The length of the connection between coil and immobilizer is restricted to 50 cm. The correct placement on the ignition lock and the exact electrical data is very important for the reading distance of transponder. The toroidal coil and receiving coil inside the transponder built a transformer. During the reading process the coil induces energy into the transponder. The transponder charges the field and generates an amplitude modulated signal with the manchester coded data. This charge of the field is demodulated inside the immobilizer. The immobilizer contains the coil driver hardware for direct connection of the toroidal coil.

The function of the immobilizer system is shared between the immobilizer control unit (ICU) and the electronic control module (ECM). The task of the Immobilizer Electronic Control unit (ICU) are:

The VIN code is calculated by the immobilizer using a random generator. The VIN code is transmitted from the immobilizer in the release message communication only in case of using an authorized key. Without an authorized key it is not possible to get the system VIN code. In case of ECM internal state is in Virgin mode or Neutral mode the ECM learns the system VIN code automatically after receiving the first release response message.

To get a synchronized immobilizer system (same VIN code in immobilizer and ECM, authorized key) the DLC test equipment has to be used for authorization of the keys (first key coding). The usage of this test equipment is restricted to authorized persons.

In the active mode of immobilizer (engine OFF, IG key OFF) the status LED is blinking as mode A. When ignition is turned ON, the system wakes up and tries to read out the transponder.

In case of the detection of a valid key, the release message communication with the ECM takes place. The status LED displays the immobilizer state "valid key".

After turning off the ignition (ignition OFF detection similar to the ECM ignition OFF detection), the immobilizer changes to the active mode. The status LED is blinking as mode A.

When the ignition is on, a scan tool can switch the immobilizer control unit (ICU) to the DLC mode for diagnostics, key coding and ID coding. The status LED is turned off during DLC mode. The immobilizer will answer all correct messages, which are defined as immobilizer messages.

One of 65,535 VIN codes is stored in the immobilizer EEPROM.

The VIN code can be erased by using "Reset VIN code" command of the scan tool.

When the immobilizer control unit calculates a new VIN code, ECM VIN code should be reset to get identical with the immobilizer control unit. During diagnostic procedures, the VIN code can be read for comparison with the ECM VIN code by using the scan tool "Read immobilizer control unit VIN code" command.

Serial data can be exchanged between a scan tool and the ECM and the immobilizer control unit.

There is a security indicator on the clock. Status LED An external LED displays the immobilizer system status. The immobilizer contains the LED driver hardware for direct connection of one LED.