The footwell module (FRM) is an electrical nodal point in the footwell on the drivers side. The footwell module picks up the signals from the doors and controls the lighting. The footwell module also controls the adaptive headlights. The footwell module is also the interface to the dashboard.
The following components deliver signals for the footwell module:
- Height sensors
- Reversing light switch
- Brake light switch
- Hazard warning flasher switch
- Light switch
- Driver’s door switch block
- Door contacts in front doors
- Driver’s door lock
A number of control units are involved in the lighting system. In a stricter sense, the following control units are involved in the lighting (in alphabetical order):
ACSM or MRS: Crash safety module / multiple restraint system
- E81, E82, E87, E89, E90, E91, E92: multiple restraint system
- E70, E71, E93: ACSM stands for ”Advanced Crash Safety Module”, also known as the Crash Safety Module
The footwell module is connected to the crash safety module / MRS control unit 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 passengers side is only activated when the front passenger 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
When cruise control is in operation, the brake lights are actuated during automatic braking (legal requirement). To do this, a signal must be sent from the DSC to the accelerator pedal module via the PT-CAN.
DSC: FLA: High-beam 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 headlights to the footwell module (FRM). On the basis of this recommendation and various other the input variables, the footwell module decides whether the main-beam headlights 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 unit. The 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 unit, the FZD control unit.
The footwell module is connected to the FZD control unit 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 option ”Active Cruise Control” uses the ”turn signal” from the footwell module to help when changing lanes. In other words, if a left turn indicator is given before overtaking, the distance to the vehicle in front 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.
RLS / RLSS: Rain/light sensor or rain/light solar sensor
> E81, E82, E87, E89, E90, E91, E92, E93: Rain/light sensor
> E70, E71: rain/light solar sensor
The rain/light sensor measures the ambient brightness outside the vehicle. Depending on the ambient lighting conditions, the footwell module will switch the driving lights 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-range adjustment for the dipped-beam headlights is actuated. In darkness, the rain/light sensor transmits the message ”Darkness”. The adaptive headlights are then activated when the vehicle is cornering.
SZL: Steering column switch cluster
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.
The following components are controlled:
- Exterior mirrors
- Power window drive
- Tail lights
- Fog lights
- Centre high-mount stop lamp
- Auxiliary turn indicator light
- Front courtesy lighting
- Rear courtesy lighting
- Number-plate light
- 2 stepper motor controllers for the adaptive headlight stepper motors
- 2 belt feeder controllers (only E92)
Seatbelt extender controller (only E92)
The footwell module (FRM) activates the two belt hand-over controllers for the drivers and passengers side. The belt hand-over controllers are connected across an LIN bus on the footwell module. The belt hand-over controller activates the drive of the belt hand-over. The position of the drive is reported back to the belt feeder controller by a Hall sensor in the drive. The end position of the extended belt feeder is recorded by another Hall sensor. The end position is indicated to the belt feeder controller. The belt feeder controller transmits both signals to the footwell module (FRM) via the LIN bus. The actuation circuit is located in the footwell module. The belt handover on the passengers side is only activated when the front passenger seat is occupied.
The following functions are executed by the footwell module:
– Gateway between LIN bus and K-CAN
– Waking by means of various signals
– Storing vehicle order
Gateway between LIN bus and K-CAN
The footwell module (FRM) enables communication to take place between the LIN bus and the K-CAN. The footwell module transfers the messages to the relevant recipient bus. Components on the LIN bus: Special equipment exterior mirrors Switch block in driver’s door, High variant 2 stepper motor controllers for the adaptive headlight stepper motors 2 belt feeder controllers (only E92)
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 Change in status of door contacts, Anti-theft alarm system triggered.
Footwell modules markings:
LOW == without fog lamps, without XENON, without AHL
NSW, BASIS == with fog lamps, without XENON, without AHL
XE == with fog lamps, with XENON, without AHL
AHL == with fog lamps, with XENON, with AHL