Transponder (built into the key)
Pic. 7.78. transponder
When the ignition is turned on, the loop antenna supplies power to the transponder, which stores power in a capacitor.
As soon as the output of energy from the loop antenna stops, the transponder transmits secret data using the stored energy.
The transponder uses an advanced coding algorithm. When programming the key, special vehicle data are entered into the transponder, which are stored in the transponder's memory. The recording is one-time, so the contents of the transponder memory cannot be supplemented or changed.
Immobilizer Antenna Unit («Smartra»)
Pic. 7.79. Immobilizer Antenna Unit
Block «Smartra» provides communication with the transponder built into the ignition key. Communication is carried out at a radio frequency of 125 kHz. Block «Smartra» installed on the ignition switch next to the frame transceiver radio antenna.
The radio frequency signal received by the loop antenna is converted by the unit «Smartra» to serial communication messages. Messages received from the engine control unit are converted into a radio frequency signal, which is transmitted through the antenna to the transponder of the key.
Block «Smartra» does not check the correctness of transponder recognition and calculation of the coding algorithm. It is only an advanced interface that converts the RF data stream from the transponder into a series of messages to the engine control unit and vice versa.
The engine control unit
Pic. 7.80. The 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. Starting the engine is possible only if the results of the algorithms match. The transponder data of all valid vehicle keys is stored in the memory of the engine control unit.
Data line connector
Pic. 7.81. Data line connector
Diagnostic codes are read by attaching a voltmeter or instrument to the connector «Hi-Scan2».
Diagnostic tool
Pic. 7.82. Diagnostic tool
The device has ICM functions («Smartra»), ECM (the engine control unit), diagnostics and key replacement.
Emergency start with diagnostic tool
If the engine control unit detects a malfunction of the unit «Smartra» or transponder, it activates the emergency engine start function in the immobilizer system. Emergency start is only possible if the user password has been previously entered into the memory of the engine control unit (4 digits). 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 seconds only if the engine control unit and the user password are in the state «programmed» and the entered user password is correct. The engine can only be started during this time, after which it becomes impossible to start.
If an incorrect user password is issued, the engine control unit rejects the start request for one hour. The duration of this deviation cannot be reduced by disconnecting the battery or by any other means. After connecting the battery, the timer starts counting from zero.
Emergency start with 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 turning 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 state «programmed» and the entered user password is correct. The engine can only be started during this time, after which it becomes impossible to start. After entering a new password, the timer starts counting the 30-second period from zero.
After turning off the ignition, the engine control unit is blocked after 8 seconds. The next start requires the user password to be entered again.
Diagnostics of malfunctions of the immobilizer
The diagnostic system controls:
- communication between the engine control unit and the unit «Smartra»;
- block operation «Smartra» and transponder;
- data stored in the memory of the engine control unit related 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, signal low/high). This classification of errors is presented in the table below.
Replacing the engine control unit and block «Smartra»
The defective engine control unit is replaced «clean» or «neutral» block. In this case, all keys must be programmed in a new block. Keys not programmed in the new unit will not work (see key programming procedure). Since transponder programming cannot be changed, vehicle-specific data must remain unchanged.
When replacing a block «Smartra» no special procedures are required. Instead of the old block «Smartra» a new one is installed. This device does not store any transponder related data.
Neutralization of the engine control unit
The engine control unit is driven by «neutral» condition with a tester.
The car key is inserted into the ignition lock, and when the ignition is turned on, its data is recorded. The engine control unit requests specific vehicle data from the tester. Communication messages are defined as «neutral mode». After successful reception of the data, the engine control unit goes into a neutral state.
The engine control unit remains locked and does not provide emergency start mode and functions «double ignition switch».
Key programming is done in the same way as for «clean» engine control unit. Due to the impossibility of changing the programming of the transponders, the special data of the vehicle must remain unchanged. To change the data, new keys with a clear transponder must be available.