Land Rover Discovery Owners & Service Manuals

Land Rover Discovery: Anti-theft - Active / Operation

Operation

The Central Junction Box (CJB) automatically arms and disarms the active anti-theft system when it operates the Central Locking System (CLS).

On vehicles without a volumetric sensor, only the perimeter mode is available to monitor the hinged panels and the validity of the smart key.

When perimeter mode is active, the CJB monitors panel ajar switches located in the latch mechanisms of the front and rear doors and the tailgate.

A separate hood ajar micro switch, located in right hood latch mechanism in the engine compartment, monitors the hood status.

When volumetric mode is active, the CJB monitors the interior of the vehicle for movement using a volumetric sensor located in the front overhead console.

Arming

On vehicles without a volumetric sensor and a tilt sensor, the active antitheft system is armed in the perimeter mode when the vehicle is either locked or double locked.

On vehicles fitted with a volumetric sensor, the system has 2 modes of operation; perimeter mode and volumetric mode.

Perimeter Mode

Perimeter mode only monitors the hinged panels and validity of the smart key in the start control module. Perimeter mode is activated by a single press of the lock switch on the smart key.

Volumetric Mode

Volumetric mode monitors the vehicle interior for intrusion. If the vehicle is fitted with a Battery Back Up Sounder (BBUS), which incorporates a tilt sensor, the vehicle attitude is also monitored when volumetric mode is active. Volumetric mode is activated by a second press of the lock switch on the smart key. The second press of the switch must occur within 3 seconds of the first press. The second press of the lock switch also activates the perimeter mode double locking feature.

The Central Junction Box (CJB) arms the active anti-theft system when it locks or double locks the vehicle, providing all the following conditions are met:

  • All doors, tailgate and hood are closed.
  • The CJB is not in transit mode.

When the vehicle has successfully completed its locking routine, confirmation will be given by a single flash of the turn signal indicators to indicate the locked condition. If double locking is activated, then the confirmation will be given by a double flash of the turn signal indicators; one flash for locked and one long flash for double locked.

Mislock

If any doors, tailgate or hood is open when a lock or double lock request is received, the active anti-theft alarm system remains disarmed and the Central Junction Box (CJB) generates a short mislock sound from the vehicle horns or Battery Back Up Sounder (BBUS) and the turn signal indicators will not flash. Each attempt to lock will be confirmed by an audible chime being emitted.

When the CJB arms the active anti-theft system, it first enables perimeter mode and monitors the status of the hinged panels. If the vehicle is fitted with a BBUS, an arming signal is sent from the CJB to enable the sounder. If the vehicle is double locked and fitted with a volumetric sensor, the CJB then sends an arming signal to the module and the tilt sensor when double locked. The CJB ignores the signals from the volumetric sensor for the first 30 seconds to allow time for the vehicle interior to settle and prevent false alarm activation.

If the tailgate is opened via the smart key, the volumetric sensor and the tilt sensor are inhibited until the tailgate is closed.

Disarming

The Central Junction Box (CJB) will disarm the active anti-theft system to prevent false alarm activation under certain conditions as follows:

  • When the active anti-theft system is armed in volumetric mode, if the vehicle battery voltage decreases to less than 9 volts, the CJB will disable the volumetric mode and remain in perimeter mode only. This prevents false alarm activation because the volumetric sensor cannot operate correctly below 9 volts.
  • On vehicles fitted with a Battery Back Up Sounder (BBUS), if the vehicle battery voltage decreases from 9.5 to 9 volts in more than a 30 minute period, the CJB de-activates the BBUS and, if required, will use the vehicle horns to sound an audible alarm trigger warning. This prevents false alarm activation. At voltages below 9 volts, the CJB will not generate the 'heartbeat' signal to the BBUS. The BBUS interprets this as the CJB has been tampered with and activates its sounder. If the battery voltage subsequently rises to more than 9.5 volts, the CJB will re-arm the BBUS
  • If the vehicle is unlocked using the unlock switch on the smart key and, within 60 seconds a hinged panel is not opened, the CJB automatically relocks the vehicle and re-arms the active anti-theft system (if the 'auto relock' feature is enabled). This prevents leaving the vehicle unlocked and disarmed by accidental operation of the smart key unlock switch.

Alarm

When the alarm is triggered, the Central Junction Box (CJB) activates audible and visual warnings. The audible warnings are produced by the security horns or the Battery Back Up Sounder (BBUS). Visible indications are produced using the turn signal indicators.

The CJB activates the vehicle horns or BBUS and the visual indications for 30 seconds. The activation is stopped for 5 seconds and, if the alarm trigger is still present, the CJB will cycle again for 30 seconds (60 seconds in certain markets). This will be repeated for up to a maximum of 10 cycles (3 cycles in certain markets) of 30 seconds (60 seconds in certain markets) for any one arming period. The CJB will ignore the trigger cause if the 10 cycles (3 cycles in certain markets) have been completed and the alarm trigger is still present or until it receives a disarm signal.

NOTE:

If the battery backed sounder is triggered due to tamper detection, the visual indication using the turn signal indicators is not activated.

The alarm can be triggered by any of the hinged panels being opened, the interior motion sensor detects a movement inside the vehicle, the tilt sensor detects vehicle movement or an ignition tamper is detected (invalid smart key).

Battery Back Up Sounder (BBUS)

When the Central Junction Box (CJB) arms the active anti-theft system, in either the perimeter mode or the volumetric mode, the CJB sends an arming signal to the Battery Back Up Sounder (BBUS) on the Local Interconnect Network (LIN) bus. When the system is armed in the volumetric mode, the CJB also sends an arming signal to the tilt sensor (if fitted).

NOTE:

If a BBUS is fitted, it is also armed with the perimeter mode lock request. However, the tilt functionality is not enabled in perimeter mode.

On receipt of the arming signals, the sounder and the tilt sensor respond with a status message. If the CJB does not receive the status signals within 12 seconds, the CJB assumes there is a fault and responds with a disarm signal to either the sounder and/or the tilt sensor and stores a related fault code. If the sounder is disarmed when the active anti-theft system is armed and the system is subsequently triggered, the CJB energizes the horn relay and uses the vehicle horns to sound the audible warning in place of the sounder.

When the sounder is armed, the CJB sends a periodic (heartbeat) signal to the sounder which prompts the sounder to monitor the vehicle battery supply and the LIN bus link with the CJB. The sounder will operate if:

  • It receives an alarm signal from the CJB or the tilt sensor.
  • The power supply or the LIN bus link to the CJB is disrupted.

The tilt sensor measures the longitudinal and lateral angle of the vehicle over a range of +-16 degrees from the horizontal. When the active anti-theft system is armed in volumetric mode, the tilt sensor stores the current vehicle angles in its memory and monitors the tilt sensor readings. If the vehicle angle changes in either direction by more than the alarm limit, the tilt sensor activates the sounder.

If the alarm system is active and the battery or the BBUS is disconnected, the sounder will operate without the visual indication of the turn signal indicators flashing.

CONTROL DIAGRAM

CONTROL DIAGRAM

A = HARDWIRED;

F = RADIO FREQUENCY (RF) TRANSMISSION;

O = LOCAL INTERCONNECT NETWORK (LIN) BUS;

AO = MEDIUM SPEED (MS) CONTROLLER AREA NETWORK (CAN) BODY BUS.

  1. Central Junction Box (CJB)
  2. Driver Door Module (DDM)
  3. Passenger Door Module (PDM)
  4. Rear Door Module (RDM) - Right side
  5. RDM - Left side
  6. Driver door latch mechanism
  7. Rear right door latch mechanism
  8. Rear left door latch mechanism
  9. Passenger door latch mechanism
  10. Tailgate latch mechanism
  11. Battery Back-Up Sounder (BBUS)
  12. Immobilizer Antenna Unit (IAU)
  13. Instrument Cluster (IC)
  14. Volumetric sensor
  15. Front overhead console
  16. Radio Frequency (RF) receiver
  17. Keyless Vehicle Module (KVM)
  18. Smart key
  19. Ground
  20. Power supply
  21. Front overhead console
  22. IAU
  23. Tailgate latch mechanism
  24. Hood switch

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