Immobilizer System
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 ECM in a 5 byte of encoded data.
These 5 bytes are composed by a mixture of random data and two types of fixed codes are:
| • | A vehicle model identification number : MIN |
| • | A vehicle specific identification : VIN |
The VIN is known from the first supply of the system.
The VIN is recognized by 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 ’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 take 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 Diagnostic
Trouble Code (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 immobilizer control unit and ECM must have a matching ID code. ID coding and key coding are accomplished by using Scanner-100.
The immobilizer system consists of the following:
| • | 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. |
| • | The immobilizer control unit (ICU) with : |
| - | Transponder modulation and demodulation unit |
| - | Driver electronic for the external status led |
| - | Serial data link hardware |
| • | The external status led for displaying the immobilizer status. |
| • | The serial data link between immobilizer and ECM. |
Electronically Coded Keys
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 electrically erasable programmable read only memory (EEPROM) and transmits data to the ICU by modulating the amplitude of the electromagnetic
field, and receives data and commands in a similar way.
Immobilizer Control Unit
The function of the immobilizer system is shared between the ICU and the ECM.
The task of the immobilizer electronic control unit (ICU) are:
| • | Reading of the input information "ignition ON/OFF" |
| • | Controlling the states LED |
| • | Controlling the transponder read/write process (modulation, demodulation, decoding, comparison of the read code with the code of the valid keys). |
| • | Communication with the ECM after ignition ON (receiving of the ECM-request and transmission of release message). |
| • | Special functions for calculation and handling of the VIN-code. |
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 incase 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.
| • | Communication with the DLC-test equipment. Main functions are the key coding procedure, the VIN- code handling and the support for system test functions. |
| • | Handling of the software watchdog |
Operation
In the active mode of immobilizer (engine OFF, IG key OFF) the status LED is not 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.
Data Link Connector (DlC) Mode
When the ignition is on, a scan tool can switch the immobilizer control unit 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. |
ID Code Handling
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’s.
During diagnostic procedures, the VIN code can be read for comparison with the ECM VIN code by using the scan tool’s "Read immobilizer control unit VIN code" command.
Serial Data Link
Serial data can be exchanged between a scan tool and the ECM and the Immobilizer control unit. The scan tool connection is the data link connector (DLC).
Electronic Control Module (ECM)
| | In this mode, the ECM knows only the model vehicle identifier code. |
| | The engine can be locked/unlocked. |
| | ECM requests to ICU the VIN number. As soon as the ECM receives two correct consecutive communication frames with the same VIN code the ECM learns it. |
| | The VIN code will be stored in non-volatile memory at the end of power latch phase. ECM enters in Learnt mode. |
| | In such a state, ECM checks on every communication, the correct encoding of the ICU. |
| | If the code received is not correct, then the vehicle is immobilized. |
| | The coded 5 bytes of data emitted by ECM are a mixture of MIN code and random. |
| | The coded 5 bytes of data emitted by ICU are a mixture of VIN code and random. |
| | This mode is a special intermediate mode, used for ICU replacement or immobilizer option installation. |
| | ECM request to ICU the VIN number. As soon as the ECM receives two correct consecutive communication frames with the same VIN code the ECM learns it. |
| | The VIN code will be stored in non-volatile memory at the end of power latch phase. ECM enters in Learnt mode. |
| • | After turning on the ignition the ECM will control the engine in a normal way for starting and running while waiting for a valid release response message from the immobilizer. |
| • | After receiving a response message including the information "ICU in learnt mode" and the correct system VIN code. |
| | The ECM enters the release state, which allows to continue the running of the engine. |
| • | After receiving a response message including the information "ICU in learnt mode" and a wrong system VIN code. |
| | The ECM does not send a new request and enters the blocked state, which causes the activation of the immobilization
actions of the engine. |
| • | If the ECM does not receive a response message within a defined time from beginning of the release time period or the ECM receives a no release answer. |
| | The ECM enters the blocked state, which causes the activation of the immobilization
actions of the engine. |
| | The inactive state of the Immobilizer (valid key/invalid key) ends with turning off the ignition. |
Security Indicator
There is a security indicator on the meter cluster.
Status LED
An external LED displays the immobilizer system status. The immobilizer contains the LED driver hardware for direct connection of one LED.
Status LED
| Immobilizer System Status
| Note
|
Blink
| Active
| Ignition OFF
|
Blink
| Active
|
|
OFF
| Inactive
|
|
Blink
| Active
|
| • | VIN Code is different between ICU and ECM is learnt state |
|
ON
| Active
|
| • | Transponder reading error |
|
OFF
| Active
|
| • | Reader exciter ASIC error |
|
