Central locking system (ZV)

The central locking system enables electrical locking and unlocking of all vehicle doors by means of the radio remote control, the door lock on the driver's door and the centerlock button in the vehicle.

Brief description of components

Car Access System (CAS)

The Car Access System (CAS) control unit contains the functions of the radio remote control, the ignition switch, the terminal control and the immobiliser. It is also the gateway module between the data buses K-CAN SYSTEM and K-CAN PERIPHERALS.

The CAS controls all the higher-order functions of the central locking system.

The centerlock button, which can be used to operate the central locking system, is also connected to the CAS.

Door modules

The door modules register the signals of the switches and sensors installed in the doors and control the drives installed in the doors. Information is received and sent via the K-CAN PERIPHERALS data bus.

System lock

Two central locking drives are integrated into the system lock. This makes it possible that the lock mechanism can be moved into three different locking positions, namely the positions ”Unlocked”, ”Locked” and ”Secured” (see chapter on main functions).

Two switches integrated in the system lock (Hall sensors) register the positions ”rotary tumbler open or closed” and the state ”door unlocked”.

The door module in the driver's door also contains two other switches (Hall sensors) that detect the positions of the door lock. The central locking system can be locked and unlocked at the door lock.

The system locks are connected by cables with the relevant door modules.

Power module

The power module monitors the vehicle voltage and the vehicle battery.

The central-locking drive for the fuel tank flap is connected at the power module.

The power module also contains the function of the boot-lid unlocking and Soft Close Automatic for the boot lid.

Key transmitter

The radio-control key contains a radio transmitter that transmits an encrypted radio signal when a key button is pressed. The radio signal is received by the rear window aerial and sent to the Car Access System.

The radio-control key can be used to operate the central locking system.

To ensure antitheft protection, the radio signals are encrypted using a random code.

Main functions

Positions of the central locking system

The two locking drives integrated in the door modules move the lock mechanisms into the following positions:

• Lock
  A locked door cannot be opened from the outside. However, the door can still be opened from the inside by pulling the door handle twice.
  The doors are locked when the central locking system is locked using the centerlock button or, in the case of operation via door lock or radio-control key, when the conditions for ”Secure” are not met (see Secure function)
  
• Secure
  A locked and secured door cannot be opened from the inside or outside.
  The vehicle is secured when the central locking system is locked using the radio-control key or the door lock is locked and beforehand, after switching off terminal R, the driver's door has been opened and closed or the passenger's door has been opened.
  If, in the case of secured central locking system, a key belonging to the vehicle is inserted in the identification lock, the central locking system changes from the position ”Secured” into the position ”Locked”. The doors can then be opened from the inside.
  The antitheft alarm system is armed when the vehicle is secured.
  
• Unlocking
  An unlocked door can be opened from the outside and inside.
  The armed antitheft alarm system is disarmed when the vehicle is unlocked.
  

The central locking drive for the fuel tank flap is activated by the power module. When the central locking system is locked, the fuel tank flap is locked; when it is unlocked, the fuel tank flap is also unlocked. As a coding variant (series status on US vehicles), the function ”fuel tank flap for secure” is available. This means that the fuel tank flap is only locked when the central locking system is secured.

Operating points

The central locking system can be operated from following points:

• Remote control key
  
• Door lock (locking cylinder) driver's door
  
• Central-locking switch (centerlock button)
  the centerlock button can be used to lock and unlock the central locking system, but not to secure it. It is only possible to lock the central locking system using the centerlock button when the front doors are closed.
  

To increase antitheft protection, operation of the central locking system via the boot lid lock is not possible. Via the boot lid lock, it is only possible to mechanically unlock the boot lid.

Safety functions

The following safety functions are performed centrally by the CAS control unit for the entire central locking system:

• Crash unlocking
  In the event of an accident, the safety system detects a crash and a crash message is sent across the CAN bus. On reception of the crash message by the CAS control unit, this sends the command to the door modules and power module to unlock the central locking system.
  To avoid unwanted central locking actions by cable short-circuits as a result of an accident, the crash detection blocks all operating locations. Operation of the central locking system following a crash is only possible after terminal R has been switched off for at least 3 seconds.
  
• Forced double unlocking
  If, in the case of secured central locking system, a key belonging to the vehicle is inserted in the identification lock, the central locking system changes from the position ”Secured” into the position ”Locked”. The doors can then be opened from the inside.
  The antitheft alarm system is disarmed when the vehicle is subjected to forced double unlocking.
  
• Lockout protector
  To protect the driver against inadvertent vehicle lockouts, all the operating locations are blocked when the driver's door is open. There are no additional mechanical lockout safety devices in the system locks.
  It is only possible to lock the central locking system using the centerlock button when both the front doors are closed.
  
• Voltage monitoring
  The functional range of the central-locking drive is set from 9 V to 16 V. Outside this range, there is no activation of the drives.
  

Anti-repeat circuit

To protect the central-locking drives against overloading, the door modules and the power module monitor the central-locking drive for repeat operation. If there are more than 32 actuations inside 2 minutes, the drives are blocked by the modules for a defined period.

The anti-repeat device is ineffective in the case of crash unlocking.

Mechanical asynchronism

If the central locking system is locked and a door is opened mechanically by means of the door handle, the electrical central-locking drive for this door is asynchronous to the lock mechanism.

This condition is detected by the door module via a switch (Hall sensor) in the system lock. The next time the central locking system is locked, this condition is remedied in that the central-locking drive in this door is first locked and then unlocked.

Country versions and coding variants

The following country versions and coding variants are possible and, in part, can be set using the Car & Key memory:

• Double-unlocking via centerlock button (country version USA)
  As an extended safety function, a secured vehicle can be unlocked with one press of the centerlock button. This does not disarm the antitheft alarm system.
  
• Locking the fuel tank flap only when vehicle is secured (country version USA)
  The fuel filler flap is only locked when the vehicle is secured.
  
• Selective central locking (series status for country version USA)
  With the first unlocking command, only the driver's door is unlocked. Al the remaining doors are only set from the position ”Secured” to the position ”Locked”.
  
• Automatic lock
  The central locking system is automatically locked when the vehicle moves. Here, the following additional coding is possible:
  Setting the speed as of which the function is executed
  Execution if vehicle was not yet locked.
  Execution if one door was unlocked.
  Execution once after driving off.
  Execution after each driving off if unlocked again in meantime.
  
• Relocking
  If the central locking system is unlocked using the radio remote control, there is an automatic locking procedure (lock and secure) after 2 minutes if no door is opened during this period.