Footwell Module

Footwell Module

The footwell module (FRM) is an electrical nodal point in the footwell on the driver's side. The footwell module activates the lighting, the front power windows and the outside mirrors. It picks up the signals of the doors, of the switch block in the driver's door and the height-level sensors. The footwell module also controls the adaptive headlights. The footwell module is also the interface to the dashboard.

Brief description of components
The following components deliver signals for the footwell module:
- Height sensors
- Brake light switch
- Reversing light switch
- Hazard warning switch
- Light switch
- Driver assistance systems operating unit
- Switch block, driver's door
- Door contacts of the front and rear doors
- Driver's door lock

A number of control modules are involved in the lighting system. In a stricter sense, the following control modules are involved in the lighting (in alphabetical order):

- ACSM: Crash Safety Module
ACSM stands for "Advanced Crash Safety Module", referred to as the crash safety module.

The footwell module is connected to the crash safety module via the K-CAN. In the event of an accident with corresponding severity, the footwell module switches on the interior light and the hazard warning lights automatically.

The crash safety module sends a message regarding the front passenger seat occupation detection on the K CAN. The belt handover on the passenger's side is only activated when the passenger's seat is occupied.

- AHM: Trailer Module
The trailer module delivers the signal indicating whether a trailer is attached to the vehicle. The trailer module also controls the trailer lighting.

During trailer towing, the trailer module automatically disables e.g. the rear Park Distance Control (PDC) and the rear fog lamp on the vehicle.

If a trailer is detected, the automatic parking function is disabled. (Automatic parking function: To improve the view of the kerb, the outside mirror glass is folded downwards when reverse gear is engaged. This brings the lower area immediately around the vehicle, i.e. the kerb, into the field of vision.)

The trailer module (AHM) is connected to the footwell module via the K-CAN.

- DSC: Dynamic Stability Control
If the cruise control is activated, the brake lights are activated during automatic braking (legally prescribed). To do this, a signal must be sent from the DSC to the accelerator pedal module via the PT-CAN.

- FLA: High beam headlight assistant
In accordance with the traffic situation, the high-beam assistant sends a switch-on recommendation or a switch-off recommendation for the high beam to the footwell module (FRM). On the basis of this recommendation and various other the input variables, the footwell module decides whether the high beam should be switched on or off.

- FRM: Footwell Module
The footwell module is connected to the vehicle with 3 plug connections. Two 51-pin connector connect the main wiring harness. Another 26-pin connector is for the connection to the dashboard.

- FZD: Roof function center
The roof function centre is responsible for the components of the interior lighting in the roof area.

The Basic variant of the roof function centre has its own control module. The front interior light and the rear-compartment interior light are activated via the footwell module (FRM). The High variant of the roof function centre has its own control module, the FZD control module.

The footwell module is connected to the FZD control module via the K-CAN.

- JBE: Junction box electronics
The lighting for the luggage compartment and the glove box lighting are connected to the junction box electronics.

- LDM: Longitudinal Dynamics Management
In conjunction with the LDM, the active cruise control optional extra uses the signal indicating from the footwell module as an aid when changing lanes. This means that when the left-hand turn indicator is operated before overtaking another vehicle the distance to the vehicle ahead is reduced. The vehicle to be overtaken is then lost more quickly. On the other hand, when changing to the right-hand driving lane, a vehicle moving there is picked up more quickly.

- RLSS: Rain/light solar sensor
The rain-light sensor measures the ambient brightness outside the vehicle. Depending on the surrounding brightness, the footwell module switches the low-beam headlight on or off. To do this, the automatic driving lights control must be activated (light switch in switch position A ). At dusk, the rain-light sensor sends the message dusk. The footwell module switches the low-beam headlight on. The automatic headlight beam height control of the low beam is activated. In darkness, the rain-light sensor sends the message Darkness. The adaptive headlights are then activated when the vehicle is cornering.

- SZL: Steering column switch center
The switch signals from the turn-signal/high-beam switch are picked up and evaluated by the SZL. The evaluated switch signals are forwarded as resistance-coded by the SZL via direct lines to the footwell module

- Switch cluster, driver's door
The switch block for the driver's door is connected to the footwell module by a LIN bus. The switch block in the driver's door contains the buttons for the power windows, the outside mirror adjusters and the folding function for the outside mirrors (only with outside mirrors as optional extras) as well as the buttons for the child locks and the rear window roller sunblind.

- Driver assistance systems operating unit
The driver assistance systems operating unit is connected to the footwell module by a LIN bus.

The operating unit contains button for the following driver assistance systems:
- Lane departure warning
- Head-up display
- Night vision
- Dynamic Braking Control
- Lane departure warning

The following components are activated by the footwell module:
- Exterior rearview mirror
- Front power window drives
- Headlights
- Taillights
- Fog lamps
- Additional brake light
- Auxiliary turn indicator light
- Front courtesy lighting
- Rear courtesy lighting
- Licence plate light
- 2 headlight driver modules for the step motors of the adaptive headlights
- Electrical steering column adjustment

System functions
The following functions are executed by the footwell module:
- Gateway between LIN bus and K-CAN
- Waking by means of various signals
- Other functions

Gateway between LIN bus and K-CAN
The footwell module (FRM) enables communication to take place between the LIN bus and the KCAN. The footwell module transmits messages on the other bus.

Components on the LIN bus:
- Outside mirrors of optional extra
- Switch block, driver's door
- Driver assistance systems operating unit
- Light switch
- Operating unit for seat memory, driver and front passenger
- 2 headlight driver modules for the step motors of the adaptive headlights

Waking by means of various signals
The footwell module (FRM) can be wakened via the following signals:
- K-CAN active
- Terminal 15 ON
- Hazard-warning switch ON
- State change of the door contacts
- Alarm of the anti-theft alarm system

Other functions
The footwell module (FRM) influences various functions in the vehicle. The following components are controlled by the footwell module:
- Exterior rearview mirror
- Exterior lights
- Interior lights
- Central locking
- Power windows

Exterior rearview mirror
The requests to adjust the mirror are sent via the LIN bus. The footwell module (FRM) receives and processes the signals via the LIN bus. Every 20 milliseconds, the footwell module queries whether there are requests from the switch block.

In the Sleep mode, the power supply is switched off. The outside mirrors cannot be actuated.

The mirror heating on the outside mirrors (optional extra) is activated by the footwell module. The corresponding information is forwarded to the electronic evaluation unit in the mirror via the LIN bus.

If a mirror memory is installed, the footwell module stores the memory position of the mirrors.

Exterior lights
The lighting function are integrated in the footwell module (FRM).
These lighting function are:
- Parking light
- High beam
- Headlamp flasher
- Turn signals
- Hazard warning lights
- Brake light
- Low beam
- Reversing lights
- Fog lamps
- Rear fog light
- Parking lamp

Besides the lighting functions, other exterior lighting functions are also integrated in the footwell module:
- Light monitoring
- Headlight beam height control
- Emergency operating mode if the footwell module should fail
- (Important lighting functions are replaced by activation of other lights if individual lights fail.)
- Home lighting
- Visual alarm after triggering of the anti-theft alarm system (the visual alarm is issued according to the coding by hazard warning lights, flashing with low beam or flashing with high beam.)
- Actuation of bi-xenon headlamps
- Activation of the step motor controller for the adaptive headlights
- Turning lights The turning lights are coupled to the adaptive headlights.

All lighting functions except the additional brake light are supplied with a pulse-modulated signal by the footwell module (FRM). This PWM signal enables a uniform brightness of the exterior lighting.

Interior lights
On vehicles without roof function centre (FZD), the footwell module actuates the interior lighting in the roof area directly. All footwell module outputs for interior lighting are pulse width modulated. This ensures that the interior lighting maintains constant brightness despite voltage fluctuations.

With standard equipment, the interior lighting comprises the following components:
- Front interior light
- Luggage compartment lights
- Glove compartment lighting
- Footwell lighting

The following components can also be installed as special equipment for the interior lights:
- Rear interior light
- Courtesy lighting

Central locking
The footwell module evaluates the status of the Hall 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 transmits a message on the K-CAN to the CAS (Comfort Access System):

Power window
The footwell module (FRM) and the junction box electronics (JBE) control the power window drives. The relays for the front power window motors are located in the footwell module. The relays for the rear power window drives are fitted in the junction box electronics.

Electrical steering column adjustment
The electrical steering column calibration enables the driver to set the optimized position of the steering wheel. There is a switch on the left of the steering column for operation.

The inclination and length of the steering column are adjusted electrically.

Power for the electrical steering column adjustment is provided via terminal 30g. The footwell module (FRM) activates the electrical steering column adjustment (FRM). When the steering column is adjusted, a Hall sensor on the steering column adjustment motor sends a signal to the FRM control module. The position of the steering column is registered by and stored in the FRM control module.

For the key memory, this means that the position of the steering column can be called up.

To support entry and exit, the inclination calibration moves to the highest position.For Easy Exit, the steering column calibration is automatically activated under the following conditions:
- Terminal R OFF
- Terminal R ON and driver's door opened (signal via door contact)
- Terminal 15 OFF with driver's door open (signal via door contact)

The steering column memory is activated under the following conditions:
- One of the two memory buttons is pressed (from terminal R ON).
- Another identification sensor is used (personalization).
Condition: The selection Last seat position after unlocking is activated in the Settings menu in the Central Information Display (CID).

In both cases, the steering column memory only moves to the corresponding memory position after terminal 15 On.

Notes for Service department

Nearly all Car and Key Memory functions are programmed inside the vehicle itself. (See Personal Profile in the Owner's Manual: individual settings for a maximum of 3 remote control modules via the display in the instrument cluster or via the Central Information Display)

Switch-on conditions
The footwell module (FRM) receives a large number of input signals that switch on the interior lighting. The input signals are read in directly by the footwell module or received via the K CAN.

The following signals switch the interior lighting ON:
- Interior lighting button pressed
- Door opened
- Unlocking using driver's door cylinder lock
- Unlocking using remote control
- Terminal 30B OFF if terminal 58g was ON for a maximum of 2 minutes beforehand
- Crash signal
- Press the lock button on the remote control if the central locking system is in central double-locking for longer than 10 seconds

The interior lighting is switched off under the following conditions:
- Secure central locking system, all doors and the luggage compartment lid are closed
- Interior lighting button held pressed for longer than 3 seconds
- Terminal 58 ON and terminal 30B OFF
- Terminal 30B ON with closed doors
- The vehicle is unlocked via the remote control and no door is opened within 20 seconds.
- Terminal 30B OFF and the door opened for longer than 1 minute
- Via diagnosis Power Down
- After 8 minutes terminal 30B OFF

As of terminal R Off, the interior lighting is switched off by the footwell module (FRM) after 8 minutes. To do so, the footwell module sends the message for consumer shutdown via the K CAN. The roof function centre (FZD) receives this message and switches the interior lighting off in the roof area. The interior lighting that is switched on directly by the footwell module is also switched off.

The footwell module provides terminal 58 g via the K CAN or via conventional wiring. Terminal 58 g is pulse-width modulated and has 2 brightness stages.
- Brightness stage for locating lights. The brightness stage for the locating lights can be set individually via the rocker switch on the steering column lever.
- Brightness stage for function indicator lamps. The brightness stage for the function indicator lamps is not dimmed and is switched on with full brightness.

As soon as the hazard-warning switch has been pressed, the lighting of the hazard-warning switch is switched to full brightness by the footwell module. At terminal 58 g, the hazard-warning switch is not lit up with full brightness. The brightness depends on the setting for the locating lights.

No liability can be accepted for printing or other faults. Subject to changes of a technical nature