BMW FRM Footwell Module – all you need to know
- Regular BMW owners who need to diagnose a faulty BMW FRM module
- DYIers who want to develop their own device for BMW
- Electrical engineers who are interested in reverse engineering BMWs
The BMW FRM at a glance
The BMW Footwell module (FRM) functions as an electrical hub or a node in the footwell on the drivers side. The FRM receives signals from the doors, it controls the lighting, it commands the the adaptive headlights and it also interfaces with the dashboard.
The BMW FRM receives signals from the following sources:
- 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
Mechanisms controlled
The BMW FRM controls the following mechanisms:
- Exterior mirrors
- Power window drive
- Headlight
- 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 on E92)
- Exterior mirrors
- Exterior lighting
- Interior lighting
- Central locking system
- Power window regulator
BMW FRM Footwell connectivity
The BMW FRM footwell module is connected to the vehicle through 3 connectors. There are two 51-pin connectors for the main wiring harness. There is another 26-pin connector that goes to the dashboard.
BMW FRM system functions
The BMW FRM Footwell module performs the following system functions:
- Gateway between LIN bus and K-CAN
- Waking by means of various signals
- Storing vehicle order
- Other functions
Control units involved in the lighting system
The following is a list of all the control units involved in the lighting system, listed in alphabetical order:
- ACSM or MRS: Crash safety module / multiple restraint system
- AHM: Trailer module
- DSC: Dynamic Stability Control
- DSC: FLA: High-beam assistant
- FZD: Roof function center
- JBE: Junction Box Electronics
- LDM: Longitudinal dynamics management
- RLS / RLSS: Rain/light sensor or rain/light solar sensor
- SZL: Steering column switch cluster
E81, E82, E87, E89, E90, E91, E92: Multiple restraint system
E70, E71, E93: ACSM (”Advanced 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, the FRM Footwell module switches on the interior light and the hazard warning lights automatically.
On the E92, 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.
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.
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.
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.
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.
The lighting for the luggage compartment and the glove box lighting are connected to the junction box electronics.
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.
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.
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.
Wrapping it up
To sum up, in this article we’ve seen the multitude of mechanisms controlled or influenced by the FRM Footwell module. We hope this article has helped you troubleshoot the weird symptoms that brought you here or that it helped you advance with your DIY project.
As always, we welcome comments and questions from our readers. If you want to share something, feel free to use the comments section below. Stay tuned for more articles on the workings of your favourite brand.
Comments (8)
Hello Vlad,
Thank you for your enlightening article. I am at my tethers end with an electrical, I think, glitch in my E93 passenger side mirror. And I am really struggling to find anyone who could shed some light on it.
I have folding, heated, mirror glass adjustable side mirrors and my passenger side one stopped folding one day.
Then a few days later I could no longer adjust the mirror itself but it would still dip when I was reversing! Then that started to work intermittent and I sometimes ended up with a downwards dipped mirror frozen in that position.
I took a chance and bought a secondhand mirror on ebay and installed it myself and it worked!
Only for a month though because yes, the mirror stopped folding last week and a few days ago it stopped adjusting but it still was dipping in reverse but would not completely go back to its memory position.
I am trying to trouble shoot: First I am checking whether the original motors on the old mirror have blown due to an electrical short by an electrician. Then I am going to check the wiring loom and connectors for broken wires, faulty connections and or corrosion on the connectors. Do you have any ideas what could be causing this? Could the FRM be at fault and if no mechanical issues have been found might it be a signaling fault in the LIN bus?
Kind regards,
Paul
Thanks for the piece on the footwell module, I found it very enlightening. I have a 2007 BMW x5 4.8i. About 2 weeks ago I realized my battery power was running low as it took a couple of tries on mornings to get the car to start. A voltage monitor on the front cigarette lighter would show about 10 volts, but once the engine started, the alternator maintained it at about 14 volts. So I knew I needed to get a new battery soon. Unfortunately, a week ago, before I got round to replacing the battery, I drove out on an evening, everything in the car was working. I parked and switched off lights. About an hour later, I attempted starting the engine, my monitor showed a voltage just under 10 volts. On the 3rd try the engine started…then I immediately noticed that there were malfunctions showing up.
(1) I had a full gas tank, but the indicator on the dash showed ’empty’. There were other error on the dash. ..I figured an instruments cluster malfunction.
(2) I also noticed that the 2 back glass wouldn’t roll up…lost connection with main control switch. Still didn’t work when I swapped the main power window switch with another identical vehicle.
(3) the climate control blower worked, I could adjust the blower speed but there was NO cooling. I had used the AC only an hour earlier and it was cooling normally.
(4) The car no longer locks; the confirmation lights blink as usual to locking and unlocking, but the doors do not actually lock. The alarm sound is very low, hardly audible.
(5) The tailgate no longer opens, even when the button on the dashboard is pressed.
I have replaced the battery, but the issues remain.
The piece I read about the footwell module makes me wonder if it was damaged due to the battery issue. However, I’m trying to understand whether that module also affects the COOLING of the airconditioner, and how.
Could the CAS module have gone bad too, or is it all a problem with the footwell module.
Most grateful for guidance on this.
Thanks for the knowledge bombs… In short, I’m getting Right and now left brake light malfunction. Is this signal terminating to the FRM? TIA
I have completely lost ALL power in my 2007 BMW 335xi. It has the big recall in 2017 for the power cable connection to the glove box fuse box. I also just re did the same process over the weekend to see if maybe it did it again and installed a new fuse box with it but unfortunately no it was not my problem! Car is still dead in the water. My next step in this matter is to replace a new JBE module in the upcoming days but wanted to get another opinion to see if that could possibly be the problem? This is my only car and it’s dead on sight. I don’t have the money to send it to the dealer. I can jump it from the jump posts on the engine just fine and will run but certain things like ac won’t work. As soon as I turn the car off there is no power at all! My battery is good and so is my distribution box on my battery! I checked all those out and am getting power. So, any chance the JBE could have this car sitting dead? Thanks for your time and help!!
Does the FRM have anything to do with sound. No radio, chime or Bluetooth. No sound at all. I tried fiber optic loop, nothing. I recently had water leaking in my driver’s footwell, caused by the sunroof drains. I have a 2008 X5, e70 3.0si.
Hi, I have a 2018 MINI Cooper CountryMan F60 and recently retrofit a SmartTrunk Opener/OEM TailGate KICK sensor into my car.
The module of the sensor has 3 wires with one each connecting to the 12v & the Ground & the last to ?LIN bus.
I am not sure what this LIN module wiring is and where exactly the Signal wire from the Kick sensor is supposed to connect to.
I have activated the coding for Kick sensor.
I have connected the LIN BUS/signal wire to the Signal Wire for the Lights control switch at the drivers bay but it does not work!.
Can U help me with this retrofit project, please?. Where should the Signal wire from the BMW/MINI Kick sensor module exactly connect to?.Thanks.
Hello, thanks for the info. Although I’m still not sure if this is the route cause for my problem.
I have a 2015 BMW series 1. About a couple of weeks ago I had an amber warning light come up “brake light control failure”…and that I could continue driving, but basically get it looked at. I booked it into the garage where I bought the car, and where it had recently been serviced. They did the diagnostics checks and weren’t able to find the fault. They tried to clear the message but it wouldn’t clear. They advised me to go to a BMW specialist and gave me their contact details.
It went there on Monday…they too did the diagnostic checks, told me that my brakes lights were continuous on! (I of course was not aware of this, or seen them on). They changed the brake control switch, reset and thought that would be it. No! Brake lights are now working correctly, but the warning light will still come on. They tried reprogramming it, checked the wires…other lights and still have no idea. He said it could be the footwell module but wasn’t 100% sure. I have noticed my anti roll back brake is not in operation, but I’m going to assume it’s because there’s a different fault.
Prior to taking it there the warning would come on as soon as I started the car. Now it pings up at some point during a drive (not always when I put my foot on the brake). I don’t want to pay all of that money to get that changed, and it isn’t the problem. I can’t believe I’m the only person this has happened to. What is your opinion?
Hi I’m getting a whining / grinding noise coming from the footwell I’m convinced it’s the frm module as it’s turned off the signal to the height sensors and the rear end has dropped . Other things such as messages telling me this is wrong that’s wrong when they’re not . Does this sound about right.