The design and purpose of the immobilizer antenna unit («Smartra») (Mitsubishi Matrix)

Transponder (built into the key)

When the ignition is turned on, the loop antenna sends energy to the transponder, which stores the energy in a capacitor.

Once the loop antenna stops producing energy, the transponder outputs secret data using the stored energy.

The transponder uses an advanced coding algorithm. When programming the key, special vehicle data is entered into the transponder, which is recorded in the transponder's memory. The recording is one-time, so the contents of the transponder's memory cannot be supplemented or changed.

Antenna unit of immobilizer ("Smartra")

The publication is borrowed from the website (www.hyundaibook.ru)

The Smartra unit provides communication with the transponder built into the ignition key. Communication is carried out at a radio frequency of 125 kHz. The Smartra unit is installed on the ignition switch next to the frame receiving and transmitting radio antenna.

The radio frequency signal received by the loop antenna is converted by the Smartra unit into serial communication messages. Messages received from the engine control unit are converted into a radio frequency signal, which is transmitted via the antenna to the transponder of the key.

The Smartra unit does not check the correctness of the transponder recognition and does not calculate the coding algorithm. It is only an advanced interface that converts the radio frequency data stream from the transponder into a series of messages to the engine control unit, and vice versa.

Engine control unit

The engine control unit checks the ignition key using a special coding algorithm, which is simultaneously programmed in the transponder and the engine control unit. The engine can only be started if the results of the algorithms match. The data from the transponders of all active vehicle keys is stored in the engine control unit memory.

Data line connector

Diagnostic codes are read by connecting a voltmeter or Hi-Scan2 device to the connector.

Diagnostic device

The device has ICM functions ("Smartra"), ECM (engine control unit), diagnostics and key replacement.

Emergency start using a diagnostic tool

If the engine control unit detects a fault in the Smartra unit or the transponder, it activates the emergency engine start function in the immobilizer system. Emergency start is only possible if the user password (4 digits) has been previously entered into the engine control unit memory. The password is selected by the vehicle owner and entered at the service station. For emergency start, the engine control unit is unlocked for 30 s only if the engine control unit and the user password are in the "programmed" state and the entered user password is correct. The engine can only be started during this time, after which starting becomes impossible.



If an incorrect user password is issued, the engine control unit rejects the start request for one hour. The duration of this rejection cannot be shortened by disconnecting the battery or by any other action. Once the battery is connected, the timer starts counting from zero.

Emergency start using ignition key

The emergency start function can also be activated using the ignition key. In this case, the user password is issued to the engine control unit by a special sequence of switching the ignition on and off. The engine control unit is unlocked for 30 seconds only if the control unit and the user password are in the "programmed" state and the entered user password is correct. The engine can only be started during this time, after which starting is no longer possible. After entering a new password, the timer starts counting the 30-second period from zero.

After the ignition is switched off, the engine control unit is locked after 8 seconds. The next start requires re-entering the user password.

Diagnostics of immobilizer faults

The diagnostic system monitors:

• communication between the engine control unit and the Smartra unit;
• operation of the Smartra unit and transponder;
• data stored in the engine control unit memory relating to the operation of the immobilizer.

Immobilizer errors are divided into three groups, each of which includes four typical errors (circuit failure, circuit range/characteristic deviation, low signal level/high level). This classification of errors is presented in the table below.

Replacement of the engine control unit and the Smartra unit

The faulty engine control unit is replaced with a "clean" or "neutral" unit. In this case, all keys must be programmed in the new unit. Keys not programmed in the new unit will not work (see the key programming procedure). Since it is not possible to change the programming of the transponders, the vehicle-specific data must remain unchanged.

No special procedures are required when replacing the Smartra unit. A new Smartra unit is installed instead of the old one. This unit does not store any data related to the transponder.

Neutralization of the engine control unit

The engine control unit is brought to the "neutral" state using a test device.

The car key is inserted into the ignition switch and its data is recorded when the ignition is turned on. The engine control unit requests specific car data from the tester. The communication messages are defined as "neutral mode". After successful reception of the data, the engine control unit goes into neutral state.

The engine control unit remains locked and does not provide emergency start mode or the "double ignition on" function.

Key programming is done in the same way as for a "clean" engine control unit. Since it is impossible to change the programming of the transponders, the special data of the car must remain unchanged. To change the data, it is necessary to have new keys with a clean transponder.