Airbag Light - What have you tried?
- Thread starter Daffy
- Start date
Decided to have a look into the will it arm or not question and can't get a definitive answer:
Reading Advanced Safety Electronics (ASE) section of BMW documentation has the following (amongst 23 pages on airbags alone....)
Airbag Triggering
Numerous crash and road tests under extreme conditions have been used to set the BMW
triggering thresholds for all possible types of accidents.
The triggering thresholds are primarily divided into 4 groups according to crash severity:
• CS 0: no crash (parking damage) CS=Crash Severity
• CS 1: light crash
• CS 2: crash of medium severity
• CS 3: severe crash
The triggering thresholds have been set depending on the crash severity and including
other factors such as direction, overlap on collision, and depending on the evaluation as to
whether the occupant was wearing a seatbelt or not.
This results in the various trigger thresholds for the activation of the various restraint systems.
Triggering in the event of errors
If a fault is detected in the seatbelt buckle detection system, it is assumed that the seatbelt
is not fastened. The triggering threshold is lowered. In spite of the fault recognition, an
attempt is made to activate the seatbelt lock tensioner.
If a fault is detected in the seat occupation detection system, it is assumed that the seat is
occupied. The restraint systems are activated.
If a fault is detected in the airbag switch, it is assumed that a child's seat is fitted. The front
airbag and side airbag on the passenger side are not triggered.
However this separate piece of info. seems to imply that if information is missig then airbags don't trigger such as:
Seat Occupancy Sensor
A seat occupancy detection mat is installed in the seat cushion of the passenger seat.
The sensor mat is identical to the mats used in previous models for the MRS systems. The
sensor system consists of pressure sensors that use an electronic evaluation unit (SBE) to
detect whether there is weight on the seat.
As of a weight of approx. 12 kg (26.4lbs.), the seat is recognized as occupied. The electronic
evaluation unit of the seat occupation mat isconnected to the SBSR satellite.
The information regarding seat occupation is required for activation of the following
functions:
• Airbag activation
• Activation of the seatbelt tensioners
My best interpretation of it all is that in some instances such as seat belt tensioners the system defaults to trigger however when an area of the system under one satellite has a fault that section does not trigger. EG if a passenger seat sensor fails then the front airbag, curtain airbag and where fitted knee airbag will not trigger.
I'd however not want anyone to take this as correct and if someone knows better welcome an update or correction.
On another tangent this too is interesting and might explain why airbag lights are difficult to reset:
Airbag warning lamp
If there is a fault and the airbag warning lamp is switched on, the mileage is also documented
in the fault code memory in the instrument cluster.
A mileage reading that has been entered can not be overwritten. For this reason, in the case
of an airbag fault, the fault code memory in the instrument cluster must also be
checked and deleted.
State Measured Value
SBSL
Measured Value
SBSR
Battery Cable OK 5V 5V
Interuption of the diagnostic connection 0V 10V
Short circuit to ground 0V 0V
Short to B+ 12v 12v
Reading this has given me an appreciation into the complexity of the system - quite amazing mix of electronics, sims, fibre optics, modules and kbus
Reading Advanced Safety Electronics (ASE) section of BMW documentation has the following (amongst 23 pages on airbags alone....)
Airbag Triggering
Numerous crash and road tests under extreme conditions have been used to set the BMW
triggering thresholds for all possible types of accidents.
The triggering thresholds are primarily divided into 4 groups according to crash severity:
• CS 0: no crash (parking damage) CS=Crash Severity
• CS 1: light crash
• CS 2: crash of medium severity
• CS 3: severe crash
The triggering thresholds have been set depending on the crash severity and including
other factors such as direction, overlap on collision, and depending on the evaluation as to
whether the occupant was wearing a seatbelt or not.
This results in the various trigger thresholds for the activation of the various restraint systems.
Triggering in the event of errors
If a fault is detected in the seatbelt buckle detection system, it is assumed that the seatbelt
is not fastened. The triggering threshold is lowered. In spite of the fault recognition, an
attempt is made to activate the seatbelt lock tensioner.
If a fault is detected in the seat occupation detection system, it is assumed that the seat is
occupied. The restraint systems are activated.
If a fault is detected in the airbag switch, it is assumed that a child's seat is fitted. The front
airbag and side airbag on the passenger side are not triggered.
However this separate piece of info. seems to imply that if information is missig then airbags don't trigger such as:
Seat Occupancy Sensor
A seat occupancy detection mat is installed in the seat cushion of the passenger seat.
The sensor mat is identical to the mats used in previous models for the MRS systems. The
sensor system consists of pressure sensors that use an electronic evaluation unit (SBE) to
detect whether there is weight on the seat.
As of a weight of approx. 12 kg (26.4lbs.), the seat is recognized as occupied. The electronic
evaluation unit of the seat occupation mat isconnected to the SBSR satellite.
The information regarding seat occupation is required for activation of the following
functions:
• Airbag activation
• Activation of the seatbelt tensioners
My best interpretation of it all is that in some instances such as seat belt tensioners the system defaults to trigger however when an area of the system under one satellite has a fault that section does not trigger. EG if a passenger seat sensor fails then the front airbag, curtain airbag and where fitted knee airbag will not trigger.
I'd however not want anyone to take this as correct and if someone knows better welcome an update or correction.
On another tangent this too is interesting and might explain why airbag lights are difficult to reset:
Airbag warning lamp
If there is a fault and the airbag warning lamp is switched on, the mileage is also documented
in the fault code memory in the instrument cluster.
A mileage reading that has been entered can not be overwritten. For this reason, in the case
of an airbag fault, the fault code memory in the instrument cluster must also be
checked and deleted.
State Measured Value
SBSL
Measured Value
SBSR
Battery Cable OK 5V 5V
Interuption of the diagnostic connection 0V 10V
Short circuit to ground 0V 0V
Short to B+ 12v 12v
Reading this has given me an appreciation into the complexity of the system - quite amazing mix of electronics, sims, fibre optics, modules and kbus
chris said:From what i was told, if the airbag light is on, the airbags WONT deploy. And the BMW mechanic who told me knew first hand apparently
You're probabbly right, but I'm trying to get beyond the 'mechanic told me' as I too have similar information from BMW service, but prefer to see some technical documentation to confirm.
Okay. Another update.
I bought a Peake R5/SRS-16 diagnostic and reset tool as it said on the site that it was compatible with the Z4 - It's not, or at least not with a 2004 model. Peake were very good and the seller has agreed to refund me after speaking to them.
Next step is to purchase the mat and attempt the repair myself. £102 is the best price i've had for the mat. Has anyone taken apart their seats and thus has experience of removing the mat?
Cheers,
Martin
I bought a Peake R5/SRS-16 diagnostic and reset tool as it said on the site that it was compatible with the Z4 - It's not, or at least not with a 2004 model. Peake were very good and the seller has agreed to refund me after speaking to them.
Next step is to purchase the mat and attempt the repair myself. £102 is the best price i've had for the mat. Has anyone taken apart their seats and thus has experience of removing the mat?
Cheers,
Martin
Daffy said:
That's a common problem. I've heard of several tools that turn out not to be Z4 compatible. My Indy dealer can do anything to BMW's but can't get into Zeds Carsoft seems to be a bit limp too. Autologic seem the only decent solution.
I can help as far as getting the squab out, but never changed the mat. I assume the sensor is inside between the leather and foam??
cj10jeeper said:
If you want I'll draft a quick guide to getting the squab out, but check if you need to first
cj10jeeper said:
It would seem so. The mechanic at the dealer told me that they've broken the mats simply by kneeling on them to fix something inbetween the seats ! Great design eh?!
Forgive my ignorance here, but.... Squab??
I'm going to be starting the seat disassembly tonight, I've not ordered the part yet as I want to have a look at the mat. BMW mechanic told me it was torn.
Squab is the correct term for the base cushion of the seat. It fits inside of the frame.
Look twice and undo torx only once. There's a lot of them under the seat and you don't want to end up with a box of Mechano
Look twice and undo torx only once. There's a lot of them under the seat and you don't want to end up with a box of Mechano
christurbo
Member
This thread is interesting. It would be good if you could post pics.
I take it the mat is only on the pass side!
I take it the mat is only on the pass side!
Hey Daffy. Got the seats home and performed the transplant... My airbag light is on too. Wahoo! 
I have a feeling I didn't leave the battery disconnected long enough however, rather than any actual hardware problem with the seats themselves. They both detect correctly when occupied and beep incessantly if the seatbelt is unfastened so I'm hoping I just triggered something with my blundering. Going to visit a local BMW specialist tomorrow to remove the fault light.
I have a feeling I didn't leave the battery disconnected long enough however, rather than any actual hardware problem with the seats themselves. They both detect correctly when occupied and beep incessantly if the seatbelt is unfastened so I'm hoping I just triggered something with my blundering. Going to visit a local BMW specialist tomorrow to remove the fault light.
Finland
Daffy said:
Daffy,
I replaced the mat in a M-sport seat a few years ago. The sensor mats have changed during the production of Z4s: I replaced my pre-facelift (2005) seats with post facelift M-seats and found the mats incompatible. Pre facelift models have a separate sensor mat module under the passenger seat whereas post facelift models have the a different mat and no module. I changed mine to pre-facelift mat and transferred the module from my old seats. Don't remember all details, but I found instructions from BMW TIS. The procedure included removing the seat, removing some of the seat trim and the seat back (large torx necessary), and finally opening the leather of the seat base. If i recall right, the TIS instructed to open the seat base leather completely, but I managed to slid in the the new mat by loosening only the rear of the leather and a few of the fixings in middle. Spent several hours doing this. IMO it was major surgery despite my endoscopic approach
DMike
Just got back from the garage and the fault is showing on mine as the driver's side seatbelt tensioner having an "open circuit". He reset the code but it keeps coming back. I wonder if it is actually a proper fault with the seat or either the fact I haven't yet wired up the proper buttons with heated seat control (doubt it) or that the connections need a good clean and re-seating (probable)
Right....I have dismantled the passenger seat and removed the sensor mat...it took over 3 hours without a diagram...those upholstery circlets are fecking lethal!
Despite what BMW told me, I cant see any breaks in the mat itself and I know they haven't fully removed it to test.
Do I take the plunge and buy a new mat?
Should I buy a 2004 mat for 2007 seats of a 2007 mat?
Should I take it to BMW and have them try the mat?
Despite what BMW told me, I cant see any breaks in the mat itself and I know they haven't fully removed it to test.
Do I take the plunge and buy a new mat?
Should I buy a 2004 mat for 2007 seats of a 2007 mat?
Should I take it to BMW and have them try the mat?