Airbag Warning light - Strange Intermittent fault

[BigZed]

2011 116d E87, N47

The issue I am experiencing is the airbag light is off when driver only is belted in the car. When a passenger sits and / or is belted in the car the airbag light comes on with the seat belt sign. When the passenger exits the car and the ignition is turned off and back on again the airbag light is off. The airbag light only comes on when the passenger sits in the car. 

No codes are stored when the airbag light is off. the fault code 93C2 - SBE seat mat is stored when the airbag light is on.

I have tried installing BMW E87 Seat Occupancy Sensor Bypass Mat Emulator Simulator, however all this does when plugged in ses off the airbag light when the ignition is on, and no one is in the passenger seat. I am unable to erase the fault code when this item is plugged in. Uninstalling it, and reconnecting the original wiring, allows me to clear the code, and ab back to the same scenario.

I thought that once the airbag fault is triggered, thw warning light stays on until the fault code is erased. What I experience is that the warning is only present when a passenger is in the front seat.

Any ideas on how to resolve this. 

[X5smw]

Hi. You have diagnosed the issue correctly.

its the occupancy sensor in the passenger seat.

possible it is a broken wire in the seat giving a high resistance which is why it’s reading faulty with the bypass switch? 

[X5smw]

Stupid question, but is the airbag switched off? This would cause there symptoms? 

[BigZed]

Are you suggesting its the sensor and not the mat. are they different components?

The bypass mat emulator is plugged in, in  place of the the mat plug, so that the mat is not connected to the wiring circuit. So I would have thought that in this condition the emulator is not functioning as expected, and is not completing the citcuit correctly. As I am unable to clear the fault code.

As I mentioned in the OP, I still dont understand why once the airbag warning has been triggered, that light goes out after the passenger has exited and the ignition has been cycled off and on. On other vehicles with airbag faults, I have experienced once triggrered the airbag light stays on even after cycling the ignition, until the fault is rectified and the code cleared.

I dont believe the passenger airbag has been disabled by the key. However I dont know if the passenger seat components have been disabled through INSTA in the ECU.

[X5smw]

Sorry, I’m getting a bit confused. 
if the light comes on when there is someone in the seat, then the mat is working and the airbag is switched off if I’m understanding correctly

 if the bypass emulator is in and the light stays on, then it’s reading as though someone is in the seat and not the other way round? That’s why you can’t clear it. 
check the airbag on/off switch and see if it makes a difference in positions. 

 

[BigZed]

I checked the switch position, airbag on. Toggled the switch between on,off and on.

After disabled, airbag light came on, when in seat.Turned off ignition, no-one in seat, airbag light on. Airbag enabled light now on without seat occupied. Fault code 93C2, unable to clear code.

Scenario differs now, because previously The airbag light only came on when there was someone sitting in the seat.

Will now try plugging the emulator back in to see if this allows me to clear the persistant fault code. 

[Greydog]

Hi Paul

A neighbour had the seat mat sensor fail and discovered 2 things (1) they are expensive  (2) the job is not straight forward (he has a 330i touring) 

He actually found it cheaper to buy a second hand seat with everything working fortunately passenger seats tend to be less worn.

As far as the fault code goes are there ant other codes associated (check the Footwell module)

Hope this helps

Dave

[BigZed]

Just been out again to the car to do a full fault code scan. 

With ignition on airbag light is off. full scan returned just the 93C2 code as not present but stored. Cleared the code from memory.

Cycled the ignition off /  on. No airbag light. full scan returned no codes. Applied load to seat, airbag light came on.

Cycled the ignition off /  on. No airbag light. full scan returned no codes.

Back to the original scenario. Still dont know where to go from here. 🤔

Dave, I agree, pressure mat is expensive, and PITA to do. It appears the mat is registering the load, but it doesnt know what to do with the signal.

Are the mat and sensor,2 different components ?