Locks: Description and Operation

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 CAS control unit is the master control unit for the central locking system.
The control units for the central locking system are:
- Car access system (CAS)
- Footwell module (FRM)
- Junction Box Electronics (JBE)

The CAS control units use the prompts from various operating points (e.g. lock barrel, ID transmitter, comfort access) to decide what needs to be done:
- Locking/deadlocking the central locking system
- Unlocking the central locking system

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:
- Door lock cylinder
- Remote control or identification signal
- Operating facility, hazard warning switch and central locking button
- Button, deadlocking on tailgate
- Hotel position switch
- Tailgate pushbutton, passenger compartment
- boot lid button on inside of boot lid
- Boot lid pushbutton, exterior
- Tailgate/tailgate lock
- Rear-window button
- Car Access System
- Junction Box Electronics
- Footwell module
- Driver's door lock
- Door contacts
- Drives in the door locks
- Drive for fuel filler flap
- Drive for the rear lid lock
- Drive for rear window locking
- Drive for electric locking of storage compartment in centre console

Door lock cylinder
The door lock cylinder allows mechanical locking/deadlocking and unlocking of the vehicle. If the vehicle electrical system should fail, the driver's door can be unlocked manually with the key (mechanical key element in the ID transmitter).

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

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. The storage compartment of the centre console in the convertible 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.







Button, deadlocking on tailgate
When the button for deadlocking is pressed, all doors and the fuel filler flap are locked and centrally deadlocked (Precondition: driver's door is closed).
The Car Access System (CAS) records the button signal of the pushbutton.
Whenever the tailgate deadlocking button is pressed while the large tailgate is open, the large tailgate is also closed by the automatic actuation of the luggage compartment lid.
The following graphic shows the button for deadlocking at the tailgate using the example of F07.







Hotel position switch
The tailgate can be separately double-locked with the hotel position switch. That means: The hotel position switch decouples the tailgate from the central locking system.
When the hotel setting is selected, the tailgate also stays locked after the vehicle is unlocked. That means: It is not possible to open the tailgate via the rear lid button in the passenger compartment, the rear lid button, outside, or the rear lid button at the infrared remote key or at the ID transmitter.
The Car Access System (CAS) is the master control unit. In other words, the Car Access System issues the release for opening. In the switch position secured, the hotel position switch connects to ground. The Car Access System (CAS) records the change in status.
The graphic below shows the example of the hotel position switch in the F01.







Tailgate pushbutton, passenger compartment
When a vehicle is unlocked and stationary, the tailgate can be opened from the passenger compartment via the tailgate pushbutton on the inside (hotel setting not engaged).
The tailgate opens when the tailgate button is pressed. Depending on the vehicle equipment, the tailgate opens due to spring force or electrically.
The Car Access System (CAS) is the master control unit. In other words, the Car Access System issues the enable for opening the boot lid.
The Car Access System (CAS) records the button signal from the passenger compartment tailgate pushbutton.
The Car Access System issues the tailgate pushbutton request on the bus connection as a message.
The junction box electronics are a bus user. According to the signal evaluation, the junction box electronics activate the direct current motor of the release drive in the rear lid lock. This trips unlocking of the rear lid lock.
The following graphic shows the tailgate pushbutton in the passenger compartment using the example of F01.







boot lid button on inside of boot lid
Depending on the series, vehicle equipment and national-market version, the following versions of the tailgate pushbutton inside are possible:
- with tailgate pushbutton (with optional equipment SA316 "Automatic tailgate activation")
- with central locking button (SA322 "Comfort Access")
- with boot lid button and central locking button (SA316 "Automatic boot lid actuation" and SA322 "Comfort Access")
- with tailgate pushbutton for closing large tailgate and tailgate pushbutton for opening tailgate further (large tailgate cannot be opened fully)

The following graphic shows the tailgate pushbutton at the inside of the tailgate for SA316 "Automatic tailgate activation" and SA322 "Comfort Access" using the example of F01.







The rear lid button at the tailgate, inside, can be used to close the opened tailgate. Pressing the tailgate button moves the tailgate in a closing direction.
The junction box electronics (JBE) evaluate the button signal of the rear lid button.
The central locking button signal is detected in the Car Access System (CAS).
When the button for deadlocking is pressed, all doors and the fuel filler flap are locked and centrally deadlocked (Precondition: driver's door is closed). Assuming a tailgate is open the tailgate is closed electrically.
The following graphic shows the tailgate pushbutton at the inside of the tailgate with a tailgate button for closing a large tailgate and a tailgate button for opening a tailgate further (large tailgate cannot be opened fully) using the example of F07.







The large open tailgate can be closed using the tailgate button for closing the tailgate. Pressing the tailgate button moves the large tailgate in a closing direction. The junction box electronics (JBE) evaluates the button signal of the tailgate button for closing the tailgate.
The Central Information Display (CID) enables the opening height of the large tailgate to be adjusted. The incompletely opened large tailgate can only be opened further using the inside tailgate button: "Open tailgate further". The HKL control unit (HKL stands for "automatic luggage compartment lid actuation") evaluates the button signal of the tailgate button for opening the tailgate further.

Outer tailgate pushbutton
The exterior tailgate switch allows the boot lid to be opened while the vehicle is unlocked and stationary (hotel position not applied).
The tailgate opens when the tailgate button is pressed. The outside rear lid button is directly connected to the junction box electronics (JBE). According to the signal evaluation, the junction box electronics activate the direct current motor of the release drive in the rear lid lock. This trips unlocking of the rear lid lock. Depending on the vehicle equipment, the tailgate opens due to spring force or electrically.
The following graphic shows the tailgate pushbutton on the outside using the example of F11.







Tailgate lock
The tailgate lock can be unlocked mechanically or electrically and then opened (hotel setting not engaged).
The lock barrel (if available) is mechanically connected with the tailgate lock via a Bowden cable. If the integrated key is inserted into the lock barrel and then turned, the tailgate lock is mechanically unlocked and the tailgate opens automatically or electrically by spring force.
The tailgate lock is unlocked electrically via the operating points (for example, ID transmitter, tailgate pushbutton on outside). The JBE control unit operates the DC motor of the release drive unit in the boot/tailgate lock, thereby unlocking the boot/tailgate lock.

NOTICE: Alarm activation when the tailgate lock is unlocked with the integrated key

If the vehicle is equipped with an alarm system (DWA), an alarm is triggered when the tailgate lock is mechanically unlocked using the integrated key (integrated in the infrared remote key or in the ID sensor). Precondition: Vehicle locked and secured via the central locking system.

Rear window button
The rear window button can be used to open the rear window if the vehicle is unlocked and stationary.
Pressing the rear window button switches the microswitch to ground. The junction box electronics (JBE) monitor the rear-window button. If the status of the rear-window button changes to Low, the rear window is unlocked and can be opened.
To unlock the window, the junction box electronics actuate the direct current (DC) motor on the release drive inside the rear window lock.
The Car Access System (CAS) is the master control unit. In other words, the Car Access System issues the enable for opening the rear window.
The following graphic shows the rear-window button using the example of F11.







CAS: Car Access System
All the rules for controlling the central locking system are integrated in the CAS control unit. The commands are transferred on the bus connection.

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 Hall effect sensors in 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 sends a message on the bus connection to the CAS control unit (CAS stands for "Car Access System").

Driver's door lock
The driver's door lock allows mechanical locking and deadlocking and unlocking of the vehicle. If the vehicle electrical system malfunctions, the driver's door can be unlocked using the mechanical key in the remote key.
The driver's door lock comprises:
- 2 drives with gearing
- Hall-effect sensor as a door contact

Door contacts
The footwell module (FRM) detects the signals from the door contacts. The footwell module forwards the signals via a bus connection to the Car Access System (CAS) and the junction box electronics (JBE).

Drives in the door locks
There are 2 drives in each door lock. The locking mechanism can be brought into the following position by the drives:
- Locking: door can still be opened from the inside
- Deadlock: Door can be opened neither from the outside nor from the inside.
- Unlocking: door can be opened from the inside and outside

Drive for fuel filler flap
The drive locks/unlocks the fuel filler flap. The junction box electronics (JBE) activates the powertrain.
If the battery is flat or faulty, the fuel filler flap can be emergency-unlocked by hand.

Drive for the rear lid lock
The drive unlocks the tailgate. The junction box electronics (JBE) activates the powertrain.

Drive for rear window locking
The drive unlocks the rear window. The junction box electronics (JBE) activates the powertrain.

Drive for electric locking of storage compartment in centre console
The drive locks the storage compartment in the centre console (for example F12). The junction box electronics (JBE) activates the powertrain.
In the event of a flat or faulty battery, the storage compartment in the centre console can be released in an emergency.

System overview
The following graphic shows the central locking system network.
The current wiring diagrams for the individual model series can be found in the ISTA diagnosis system (Integrated Service Technical Application).











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 central locking system incorporates the following functions:
- Locking
- Deadlocking
- Unlocking
- Hotel setting
- Crash unlocking
- Forced deadlock release
- Lockout protection
- Repeat interlock
- Automatic relocking
- Voltage monitoring
- Selective unlocking
- Speed-dependent locking
- Locking the fuel filler flap

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 effected by pressing the central locking button (Precondition: front doors be closed).

Locking
A deadlocked door cannot be opened from the inside or outside. A door is deadlocked if the vehicle is locked via the drivers door lock cylinder or the remote control.
Preconditions:
- Terminal 30B OFF
- Driver's door or front passenger door was opened
- Driver's door closed

When the vehicle is deadlocked, the alarm system (DWA) is also activated.

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.

Hotel setting
When the hotel setting is selected, the tailgate also stays locked after the vehicle is unlocked. For hotel position to be selected, the setting of the hotel position switch is detected.

Crash unlocking
A crash is identified by the ACSM control unit (ACSM stands for "Advanced Crash Safety Module", referred to as the "Crash Safety Module"). A crash message is transmitted by the CAS control unit. The message is transferred on the bus connection. The CAS control unit 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.
After a crash, the central locking cannot be operated again until Terminal 30B 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 (doors, tailgate, fuel filler flap, rear window, glove box and storage compartment in the centre console) against overloading, the Car Access System (CAS) monitors repeat operation. 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 a specified time (for example 2 minutes), the vehicle is automatically locked again (locked and deadlocked). This function can be activated via the personal profile.

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. The central locking system sets all other doors from deadlock to lock. The alarm system (DWA) is switched off and the doors remain locked. With a second unlocking command, the remaining doors are unlocked. 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 in the Personal Profile (depends on national-market version concerned).

Locking the fuel filler flap
The fuel filler flap is only locked when the central locking system is set to deadlock. This function can be activated in the Personal Profile (depends on national-market version concerned).

Notes for Service department

General notes

Almost all the functions of the Personal Profile are adjusted in the vehicle itself.