IMMOBILIZER SYSTEM
The purpose of the IMMO system is to provide and additional anti-theft to the vehicle which is installed in, preventing it from an unauthorized use. Checking of user authorization is done by use of an ignition key whose head integrates a crypto-transponder.
The Described system is a transponder-based immobilizer for an automotive vehicle.
The products constituting the application are the following ones :
| • | Up to 4 ignition keys with transponder integrated in the key head. |
| • | The antenna (toroidal coil) for energizing and communicate with the transponder with its integrated electronic modulator/demodulator driver. |
| • | The ISU control unit (Intelligent Switching Unit), in which Immobilizer function is managed. |
| • | The ECM control unit (Engine Control Management). |
| • | The external status indicator (LED) for displaying the Immoblilzer status. |
| • | The serial data link between ISU and EMS control unit.. |
| • | The data link and supply link between ISU control unit and antenna Plus the standard components, conforming to Diagnostic standard Keyword Protocol 2000 . |
| • | The serial data link (K line) between Tester and vehicle ECM (Electronic Control Module). |
Only Immobilizer related requirements of the ISU control unit and ECM control unit are described in this document.
KEY WITH INTEGRATED TRANSPONDER
The key is constituted with a mechanical part (metallic key), a transponder component. and a top and bottom shells. For the Radio Frequency Remote Control key (FR/TR key), the key contains also an electronic transmitter PCB, a buttons set and a battery.
The used transponder is the TIRIS DST crypto transponder.
ANTENNA(TOROIDAL COIL)
The antenna is a toroidal coil allowing to create the electromagnetic field necessary for transponder operation. The antenna is mounted at the ignition lock. It is connected to the antenna driver (electronic PCB integrated in the body of the coil).
This driver is connected to the ISU control unit with a four terminal connector.
The antenna is used for transponder operation, based on a sequential function principle :
| • | Transponder powering (charge) phase, during which the antenna generates an electromagnetic field using a frequency of 134.2 kHz ; this field induce energy into the transponder by way of this resonant circuit. |
| • | Write phase : used to transfer commands, addresses and data to the transponder ; the principle is a pulse width modulation of the previous electromagnetic field. |
| • | Read phase : the antenna is used as receiver, which demodulates the transponder response signal which is modulated using Frequency Shift Keying. |
ISU(INTELLIGENT SWITCHING UNIT)
The ISU is the Car-body control unit, which realizes some functions as actuators control, vehicle access control or alarm function.
The Immobilizer function is shared between the ISU and the ECM control units.
The Immobilizer tasks of the ISU are :
| • | Communication with the key’s transponder after Ignition ON transition (identification and authentication of the key, learning of the keys). |
| • | Communication with the ECM control unit after Ignition ON transition (receipt of the ECM request and transmission of release message). |
| • | Control of the Immobilizer status indicator (LED). |
| • | Communication with the Diagnosis tester (keys learning, diagnostic). |
The Immobilizer function of ISU control unit has three main modes :
| • | The Immobilizer active mode, selected when Ignition key is OFF. In this mode, the status indicator (LED) is driven in mode A or B (see Status indicator chapter), depending of the Alarm function status (armed of disarmed), (cranking is not possible). |
| • | The Nominal mode, selected when Ignition key is switched ON and Nominal mode condition is verified. It is the current mode of use. In this mode, 2 function states are considered : |
| • | Blocked state : in this state, the vehicle should be immobilized (cranking is not possible). |
| • | Released state : in this state, the vehicle can be mobilized (cranking is possible) |
| • | The Learning mode, selected when Ignition key is switched ON and Learning mode condition is verified. |
SERIAL DATA LINK
Serial data can be exchanged between a scan tool, electronic control module (ECM), and the intelligent switching unit (ISU). The scan tool connection is the data link connector (DLC).
ELECTRONIC CONTROL MODULE (ECM)
When the electronic control module (ECM) detects that the ignition is being turned ON, the ECM waits for a release message from the intelligent switching unit. If a release message is not received within a specified time, the ECM disables the engine.
The engine is also disabled if the identification (ID) code transmitted by the intelligent switching unit does not match the code stored in the ECM’s memory. Immobilization remains in effect until the ignition is turned OFF or battery power is removed.
To prevent the vehicle from being driven, the ECM applies the following strategy:
| • | The ignition module is put in a bypass mode. |
| • | The ECM will not create an electronic spark timing (EST) output, so no spark will be generated by the ignition coil |
| • | The ECM will not enable the fuel pump |
| • | The ECM will not enable the fuel injectors |
Serial data communication is transmitted on a single wire between the intelligent switching unit and the ECM.
During diagnostic procedures or ID code changing, a scan tool is added to the communication system.
An ECM with an intelligent switching unit is not exchangeable with the ECM without an immobilizer control unit
