Anti-Theft - Passive
Anti-Theft - Passive
Component Locations
General
The passive anti-theft system provides a secure interface, between the ignition key and the ECM (engine control module), to prevent unauthorized starting of the engine and immobilize the vehicle. The same system is installed for all engine variants. Each passive anti-theft system consists of the following:
^ A transponder in the head of each ignition key.
^ A transponder coil around the ignition switch.
^ A passive anti-theft system in the CJB (central junction box).
The passive anti-theft system also uses:
^ The alarm indicator, to show the passive anti-theft status.
^ The instrument cluster, as a gateway for communications with the ECM.
Operation of the passive anti-theft system is automatic and requires no input from the driver. The engine management system will only crank and run the engine when a valid key is in the ignition switch.
When it senses a key in the ignition switch the CJB (central junction box) energizes the transponder coil, which activates the transponder. The transponder transmits identification and rolling code data to the CJB (central junction box). The CJB (central junction box) checks the data from the transponder against stored data to validate the key. When the ignition switch is turned to position II (ignition), the ECM (engine control module) sends a start authorization request to the CJB (central junction box). If the key is valid the CJB (central junction box) grants the request and the ECM (engine control module) will subsequently crank and run the engine. If the key is invalid, the CJB (central junction box) refuses the request and the ECM (engine control module) will not crank the engine.
Transponder
The transponder is an integral part of the PCB (printed circuit board) located within the head of the ignition key.
The transponder is powered by a rechargeable battery and is contained within the processor on the PCB, which also controls the remote operation of the CLS (central locking system). A separate coil on the PCB is used by the transponder to receive the signals from the transponder coil on the ignition switch. The coil is also used to generate the current required to recharge the battery.
The transponder has a 256 byte EEPROM (electrically erasable programmable read only memory), which is programmed with vehicle identification data and a unique identification code. This information is stored in one of 30 key 'slots' within the CJB (central junction box). When energized, the transponder emits the coded information which is received by the CJB (central junction box). The CJB (central junction box) checks that the key is valid by confirming the received data before granting permission to start the engine. The information programmed into the transponder cannot be overwritten. If a key is lost or is no longer required, T4 can be used to disable the key to prevent it being used on the vehicle.
Transponder coil
The transponder coil is located in a plastic housing which surrounds the ignition switch barrel. The transponder coil is connected via two wires to the CJB (central junction box). The CJB (central junction box) emits electrical energy to the transponder coil which transmits data at a frequency of 125 kHz. This electrical energy excites the transponder in the ignition key when it is within 20 mm (0.78 in) of the transponder coil.
CJB (central junction box)
The CJB (central junction box) is the main component in the passive anti-theft system. The CJB (central junction box) contains a processor and software which controls the passive anti-theft system. The CJB (central junction box) is connected to the medium speed CAN (controller area network) bus, which it uses to communicate with the ECM (engine control module) via the instrument cluster and the high speed CAN (controller area network) bus.
When the ignition key is placed in the ignition switch key barrel, the passive anti-theft system wakes up. The transponder coil is activated causing the transponder to transmit its coded data. The CJB (central junction box) validates the data and transmits another request for the data. When this is received for a second time, the CJB (central junction box) confirms the key as valid.
Replacement CJB (central junction box) s are not stock items and can only be installed on the vehicle for which they were ordered. After replacement of a CJB (central junction box) :
^ Car configuration information from the instrument cluster is automatically transferred to the new CJB (central junction box).
^ T4 must be used to ensure that only those ignition keys currently in use with the vehicle are enabled in the CJB (central junction box).
Alarm indicator
The alarm indicator is located in the instrument cluster, below the tachometer. The alarm indicator provides information about the status of the active and passive anti-theft systems. Operation of the alarm indicator is controlled by the CJB (central junction box) using a hardwired connection with the instrument cluster.
For passive anti-theft system status, when the active anti-theft system is disarmed and the vehicle is immobilized (key out of ignition switch), the alarm indicator flashes once every 2 seconds. When the active anti-theft system is disarmed and the vehicle is mobilized, the alarm indicator performs a 1 second confirmation flash (when the ECM (engine control module) confirms to the CJB (central junction box) that it is in the mobilized state) and then remains off.
Control diagram
NOTE: A= Hardwired connection; D = High speed CAN (controller area network) bus; N = Medium speed CAN (controller area network) bus
