Power Locks: Testing and Inspection
Central Locking System
Central locking system
The central locking system is split over several control units. The Car Access System (CAS) monitors all the processes in the central locking system. The Car Access System is the master control unit for the central locking system.
The control units involved in the central locking system are:
- Car access system (CAS)
- Footwell module (FRM)
- Junction Box Electronics (JBE)
Brief component description
NOTICE: Central locking system equipment varies depending on the model series, model, vehicle equipment and national-market version.
The following description does not go into detail about all possible equipment ranges of the central locking system (in dependence on the model series, model, vehicle equipment and national-market version). The following components are described for the central locking system:
- Driver's door lock
- Door contacts
- Remote control or identification signal
- Central locking button
- Inner tailgate pushbutton and outer tailgate pushbutton
- Glove compartment button
- Car access system (CAS)
- Junction Box Electronics (JBE)
- Footwell module (FRM)
Driver's door lock
The driver's door lock allows mechanical locking and deadlocking of the vehicle. If the vehicle electrical system malfunctions, the driver's door can be unlocked using the mechanical key in the remote key.
Door contacts
The footwell module (FRM) detects the signals from the door contacts. The footwell module forwards the signals via the K-CAN to the junction box electronics (JBE).
Remote control or identification signal
The remote key is the key for the central locking system. The remote-control unit can be used to unlock and lock or deadlock the vehicle with radio-frequency signals (radio interface).
The ID transmitter serves as the key in vehicles with Comfort Access. If the vehicle is equipped with Comfort Access, the vehicle can be unlocked or locked without active use of the ID transmitter and the engine can be started.
The remote key is described in the text below. The description also applies to the ID transmitter.
When the unlocking or locking button is pressed on the remote key, it transmits an encrypted radio signal. The RCS aerial (RCS stands for "Remote Control Services") forwards the remote control signal to the remote control receiver.
The remote control receiver has a transmitter/receiver module. This enables bidirectional communication to be established between remote key and remote control receiver. The radio signal is then demodulated, processed and checked in the remote control receiver. That means: The radio signal from the remote key contains a vehicle-specific constant "value" which is checked by the remote control receiver. This information is only passed down the direct line connection to the Car Access System (CAS) if this value is correct. This means: Radio signals from remote keys for other vehicles (including from the same product line) will not 'wake up' the Car Access System.
Authentication of the remote control signal is then performed within the Car Access System. If the request is duly authorized, the Car Access System wakes up the vehicle and either locks or unlocks the vehicle, as appropriate.
The following components are unlocked or locked:
- Doors
- Tailgate
- Fuel filler flap
- Glove box
Operating facility, hazard warning switch and central locking button
The hazard warning switch and the central locking button are combined in a single component. Using the central locking button, the vehicle can be locked or unlocked from the passenger compartment (prerequisite: both front doors closed).
The following are locked or unlocked:
- Doors
A locked door cannot be opened from the outside. However, the door can still be opened from the inside. To do this, the inner door handle must be pulled twice.
Depending on the national-market version, opening of the door in this case triggers an alarm system (DWA).
- Tailgate
The fuel filler flap is not locked.
It is not possible to use the central locking button for double-unlocking and deadlocking.
Pressing down on the central locking button forwards the button signal via a direct line connection to the junction box electronics (JBE).
If all preconditions are satisfied for locking or unlocking, the junction box electronics activates the central locking drive on the doors and the central locking drive at the tailgate.
Inner tailgate pushbutton and outer tailgate pushbutton
Using the two buttons (inner tailgate pushbutton and outer tailgate pushbutton) it is possible to open the tailgate when the vehicle is unlocked and stationary.
The inner tailgate pushbutton is installed in the centre console control panel. The centre console control panel outputs the button signal as a request to the IHKA control unit. The IHKA control unit serves as a data interface and outputs the request as a message on the bus connection to the junction box electronics (JBE).
The junction box electronics evaluates the button signals of the two buttons (inner tailgate pushbutton and outer tailgate pushbutton). The junction box electronics activates the opening of the tailgate.
Glove compartment button
The glove box is unlocked electrically by pressing the glove compartment button. After unlocking, the two glove box covers are automatically opened by spring force.
The glove compartment button is connected via a direct line connection to the junction box electronics (JBE). The junction box electronics evaluate the button signal. The junction box electronics activates the unlocking and thus the opening of the tailgate.
CAS: Car Access System
All the functions for controlling the central locking system are integrated into the CAS control unit. The commands are transferred via the K-CAN to the junction box electronics (JBE).
JBE: Junction Box Electronics
The junction box electronics are the executing control unit for the central locking system. The junction box electronics handle activation of all the central locking drives.
The junction box consists of the junction box electronics and the power distribution box.
FRM: Footwell module
The footwell module evaluates the status of the door contacts. When the vehicle is locked or unlocked with the mechanical key element, the footwell module will recognize this request. The footwell module transmits a message on the K-CAN to the CAS control unit.
System overview
The following graphic shows the central locking system network.
System functions
NOTICE: Central locking system functions vary depending on the model series, model, vehicle equipment and national-market version.
The following description does not go into detail about all possible system functions of the central locking system (in dependence on the model series, model, vehicle equipment and national-market version).
The following system functions are described for the central locking system:
- Locking
- Deadlocking
- Unlocking
- Crash unlocking
- Forced deadlock release
- Lockout protection
- Repeat interlock
- Automatic relocking
- Voltage monitoring
- Selective unlocking
- Speed-dependent locking
- Unlocking the glove box
Locking
A locked door cannot be opened from the outside. However, the door can still be opened from the inside. To do this, the inner door handle must be pulled twice.
Locking is initiated under the following preconditions:
- Both front doors closed
- Central locking button pressed
Deadlocking
A deadlocked door cannot be opened from the inside or outside. The deadlocking function is executed when locks are engaged either at the driver's door lock barrel or using the remote key.
When the vehicle is deadlocked, the alarm system (DWA) is also activated (if installed).
NOTE: The deadlocking function is no longer available in all vehicles
Starting from 09/2008, the deadlocking function is no longer available on all vehicles. The following vehicles are still equipped with the deadlocking function:
- All right hand drive vehicles
- all vehicles for the Nordic region (Sweden, Norway, Denmark, Finland, Latvia, Lithuania, Estonia)
- all vehicles equipped with an alarm system (DWA)
Unlocking
An unlocked door can be opened from the inside and the outside. When the vehicle is unlocked, the alarm system (DWA) is also deactivated. In the event of a power failure, the driver's door can be unlocked using the mechanical key in the remote key.
Crash unlocking
A crash is detected by the ACSM safety system (ACSM stands for "Advanced Crash Safety Module", referred to as the "crash safety module"). A crash message is transmitted to the CAS. The message is sent on the K-CAN.
The CAS unlocks the vehicle. All operating points are disabled when there is a crash message. This prevents unintentional actions of the central locking system from occurring due to line short circuits caused by the accident.
The central locking system can only be reactivated after a crash once terminal R has been switched off for at least 3 seconds.
Forced deadlock release
When the Car Access System (CAS) detects that a remote key is locked in place in the insertion slot, the central locking system is double-unlocked. The central locking system assumes the "Lock" position. The anti-theft alarm system is also deactivated during forced release.
Lockout protection
To protect the driver against unintentionally locking himself out, all operating points are locked when the driver's door is open. This makes any additional mechanical lockout protection in the door locks unnecessary.
Repeat interlock
To protect the central locking drives against overloading, the Car Access System (CAS) monitors repeat operations. The doors, tailgate, glove box and fuel filler flap are monitored. If there are more than 15 attempts at activation within one minute, the drives are not unlocked for a certain time.
Automatic relocking
If the central locking system is unlocked using the remote key and no door or tailgate is opened within two minutes, a locking procedure is automatically carried out again.
Voltage monitoring
The functional range for the central locking system is specified as being from 9 to 16 volts. The drive units are not activated outside this range. If the voltage supply is interrupted, the state of the central locking system does not change (anti-theft protection).
Selective unlocking
The first time there is an unlocking command, only the driver's door is unlocked. At all other doors the central-locking system switches from deadlocking to locking. The alarm system (DWA) is switched off and the doors remain locked. The remaining doors are unlocked when the unlocking command is given a second time. This function can be activated in the Personal Profile (depends on national-market version concerned).
Speed-dependent locking
The central locking system is automatically locked from a driving speed of approx. 16 km/h. This function can be activated via the personal profile.
Unlocking the glove box
The glove box is electrically unlocked by pressing the glove box cover. The glove box has a two-section lid. After unlocking, the two glove box covers are opened automatically by spring force. The two glove box covers are interconnected by a mechanical system. It is sufficient to push only one glove box cover closed. The glove box is linked to the central locking system. On unlocking the vehicle, the glove box is also unlocked. On locking the vehicle, the glove box is also locked, i.e.: opening the glove box using the glove compartment button is not possible.
- Glove box lock, versions up to 09/2009
The following graphic shows the functional networking of the lock for the glove box, versions up to 09/2009.
- Glove box lock, version from 09/2009
The following graphic shows the functional networking of the lock for the glove box, versions from 09/2009.
Notes for Service department
Almost all the functions of the Personal Profile are adjusted in the vehicle itself.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.