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Flug540
04-14-2012, 01:13 PM
A while ago my air bag light came on. I reset it twice over a period of time and every time it came back on. I finally read the code and it came back as INPA error 24, "passenger occupancy sensor", "communication fault", "interruption of the seat pad". To verify if that indeed was the occupancy sensor I made a bypass hack as shown in this video:

How to bypass BMW Passenger Seat Occupancy Mat sensor for passenger Airbag (http://www.youtube.com/watch?v=M6HsUapqNs4)

After resetting the air bag once again and driving with the bypass contraption for over two weeks, the light did not come back. Today I decided to get the sensor out and examine it, here's what happened.

https://lh6.googleusercontent.com/-JOl--x9_1mQ/T4nNElJuGkI/AAAAAAAAA70/S1lfKqbS7qc/s800/01_1280x1024.jpg

https://lh6.googleusercontent.com/-srAHDYOSX7k/T4nNEmgG1EI/AAAAAAAAA7w/Z66vnptlBCA/s800/02_1280x1024.jpg

https://lh4.googleusercontent.com/-ZskxbQ9NmPk/T4nNFCB-9xI/AAAAAAAAA8A/Oe1iAZVhRuU/s800/03_1280x1024.jpg

https://lh4.googleusercontent.com/-QNe5gKn-iqg/T4nNG9ufxvI/AAAAAAAAA8U/8H7mFum9W9c/s800/04_1280x1024.jpg

This is where the sensor plugs in:

https://lh5.googleusercontent.com/-zsI8kISaCXM/T4nNFVyqg3I/AAAAAAAAA8I/etPT58T8lRg/s800/05_1280x1024.jpg

This is how I found the sensor, not flat on the face of the seat. I suspect that's what contributed to the failure.

https://lh3.googleusercontent.com/-tDbOcmBtWH8/T4nNHIfF85I/AAAAAAAAA8g/u9JCdLDrvpo/s800/06_1280x1024.jpg

View of the sensor as it lays more or less flat:

https://lh3.googleusercontent.com/-NJ_xOTt5mHo/T4nNG-UWgbI/AAAAAAAAA8Q/0s3hcgZ0JRU/s800/07_1280x1024.jpg

The diode tests good:

https://lh6.googleusercontent.com/-0qw_0oEZ7iU/T4nNII7cDyI/AAAAAAAAA8s/Ja2FGpu1nyU/s800/08_1280x1024.jpg

The pad with no load shows around 305K:

https://lh5.googleusercontent.com/-1IdVZdFmoNM/T4nNIPyz5VI/AAAAAAAAA8o/aqHperJwJwU/s800/09_1280x1024.jpg

However, if I briefly press hard with my finger on one of the round sensors in the pad and release, resistance reads around 42K. Not sure how to explain this.

https://lh3.googleusercontent.com/-K4L0UsbldZQ/T4nNIeOErtI/AAAAAAAAA8w/ml4BcZ9AjTg/s800/10_1280x1024.jpg

At this point I don't see any obvious failure and almost tempted to put it back (flat against the seat this time) and see what happens. At the same time, it did seem to fail accordingly to the computer... I suspect that the failure is in one of the wires inside the plastic where the contact disappears if the pad is bent a certain way in a certain place.

Does anyone know what resistance should a good pad show with and without the load?

1BadE39
04-14-2012, 04:25 PM
holy s#!% wow I thought I was thorough! I have the same problem in my 540. I reset it twice already and I do believe the culprit is any passenger over 250lbs. Is what sets the sensor off.

doru
04-14-2012, 05:21 PM
The easiest way to fix the problem is with the airbag occupancy sensor bypass. I have one just in case. What it does, it will have the airbag on at all times as opposed to only when someone sits in the passenger seat. The OEM occupancy sensor will degrade over time and it's expensive to replace. This by-pass sensor is cheap and efficient.
Purchased it from this seller (http://www.ebay.com/itm/BMW-AIRBAG-LIGHT-PASSENGER-SEAT-SENSOR-MAT-OCCUPANCY-RECOGNITION-EMULATOR-BYPASS-/220986641037?pt=LH_DefaultDomain_0&hash=item3373d48a8d).

http://i.ebayimg.com/t/BMW-AIRBAG-LIGHT-PASSENGER-SEAT-SENSOR-MAT-OCCUPANCY-RECOGNITION-EMULATOR-BYPASS-/00/s/NjMzWDYzMQ==/$(KGrHqZHJCgE9sGM8PkUBPcK04O)mQ~~60_12.JPG

DinanBimmer
04-14-2012, 06:05 PM
I have this same problem. I'd also like to remove my seats to thoroughly clean the carpets but I'm always afraid something will get messed up if I do. How long would it take me to remove the front seats and is it difficult?

QSilver7
04-14-2012, 06:24 PM
There's an excellent DIY on www.e38.org with step by step instructions and pics on how to remove the front seats...except the DIY is about installing heated seats. But, in this case, to do the install..Rhett had to remove the seats.

To quickly find the DIY...use your browsers page search (usually Ctrl+F on most PCs) and type "Rhett" for the search word...your browser should jump directly to "Rhett's front heated seat install" DIY. And don't worry..the e38 & e39 share the same front seats...so everything will be the same.

edjack
04-14-2012, 07:21 PM
In my case, the Peake SRS scan tool pointed to the "passenger seat occupied" sensor. As a lark, I unplugged and plugged the two connectors on the sensor module at the bottom rear of the seat. The problem went away so far.

In the TIS, BWM recommends the use of a snake oil called Stabilant 22 for use on troublesome low-voltage connectors to cure weird electrical happenings. I've used this stuff on other electrical connectors to mixed results. I am amazed that the Germans would endorse such a product; apparently, they must have determined that it works.

cn90
04-14-2012, 07:23 PM
I HAD the exact same issue. This is a worthless feature (occupancy sensor) from BMW engineering. Search and you will find out this is a worthless feature.
Many cars out there do not have this feature.

Once you are in a frontal collision severe enough (deceleration more than 7G), the driver airbag will deploy. By that time, in 99% of the cases, the car is totaled per insurance company.

My advice is to bypass it. Don't waste your time fixing the seat sensor.
I bought the "Seat Sensor Emulator" from ebay seller "radzos" for $10 + shipping $4.95
Works like a charm. See post #6 in this DIY. It is a 5 min mod!


DIY: 1998 BMW 528i, Replacing Driver Seat Belt Buckle (Pretensioner)
http://www.bimmerfest.com/forums/showthread.php?t=602138.

edjack
04-14-2012, 07:26 PM
Does this disable the passenger airbag?

Topaz540i
04-14-2012, 07:47 PM
i was planning on possibly getting a new driver seat butt cushion peice as mine is kinda dead. i see in your pic you peeled the leather back basically doing everything i would have to do.

how hard is it to do this and then reinstall the leather nicely?

DinanBimmer
04-14-2012, 08:28 PM
There's an excellent DIY on www.e38.org with step by step instructions and pics on how to remove the front seats...except the DIY is about installing heated seats. But, in this case, to do the install..Rhett had to remove the seats.

To quickly find the DIY...use your browsers page search (usually Ctrl+F on most PCs) and type "Rhett" for the search word...your browser should jump directly to "Rhett's front heated seat install" DIY. And don't worry..the e38 & e39 share the same front seats...so everything will be the same.

Thanks :thumbup:

Flug540
04-14-2012, 09:08 PM
The easiest way to fix the problem is with the airbag occupancy sensor bypass.

If you want to do the bypass, all there is to it really is a 1N4007 diode and a couple of 200 ohm resistors, which shouldn't cost more then $3 or so:

https://lh3.googleusercontent.com/-0J2WeLfyLv8/T4pFEC0k-nI/AAAAAAAAA9g/_GK1cI38hqc/s800/Schematic.jpg

Personally, I think the bypass is fine for testing purposes, but not as a permanent solution.

I have this same problem. I'd also like to remove my seats to thoroughly clean the carpets but I'm always afraid something will get messed up if I do. How long would it take me to remove the front seats and is it difficult?

i was planning on possibly getting a new driver seat butt cushion peice as mine is kinda dead. i see in your pic you peeled the leather back basically doing everything i would have to do.
how hard is it to do this and then reinstall the leather nicely?

I used this DIY: Heated Front Seat Install - complete (MANY pics) (http://www.bimmerboard.com/forums/posts/135542) and it was really easy and took probably about an hour to get the sensor pad out. Basically, the seat is held by four T50 bolts to the floor, one electrical cable/plug. Then remove side covers from the seat and unhook leather.

I played with my pad a bit more and I believe I found and fixed the problem. As I mentioned, I found my sensor pad not flat against the seat, but folded onto itself, which caused bending of the conductors between the four arrays of sensors (one such location circled in red):

https://lh6.googleusercontent.com/-Z-uSOfC4j_Q/T4o9gXdiSOI/AAAAAAAAA9M/vWN__kkpHxU/s800/06_1280x1024_circled.jpg

I connected the multimeter to one of the wires and to one of the legs of the diode and started wiggling the pad. It turned out that the location circled in red had damage to one of the conductors (the resistance would vary as I moved the pad). I used heat gun to straighten out the plastic at the location and it seemed to have restored the conductor probably to 98%. I'm going to put it back in tomorrow and see how it behaves. BTW the damaged location is the one that is closest to the door, so it's subjected to the most use/abuse. I believe in my case the fact that the sensor was not properly installed caused it to fail.

cn90
04-15-2012, 06:14 AM
Does this disable the passenger airbag?

No, actually it is the opposite.

This is my understanding: this whole thing about pass seat occupancy sensor is to prevent injury to a child < 40 lbs in a car seat placed in the FRONT seat.

Factory Setup:
- Adult Passenger FRONT Seat: sensor tells SRS computer that there is an adult there, in a collision with more than 7G deceleration: pass airbag deploys.
- No adult: if sensor does not sense anything more than 40 lbs: pass airbag will NOT deploy to prevent potential injury to a child (should there be a child less than 40 lbs there).


My mod using "Emulator":
- The Emulator simulates condition that there is an adult there. So in a collision, the airbag WILL deploy regardless if there is any pass in the front seat.
(I confirmed this with the ebay seller).

- So if you install this Emulator, do not place any child seat on the front.
Actually, if one searches the internet, even the government strongly recommends that in any cars, a child less than 40 lbs to be placed in the REAR seat, it is much safer there.
It does not matter what car you drive, a child less than 40 lbs do NOT belong in the FRONT seat anyway!

I am a safety-conscious person and I am confident using this mod.

QSilver7
04-15-2012, 06:43 AM
...I used this DIY: Heated Front Seat Install - complete (MANY pics) (http://www.bimmerboard.com/forums/posts/135542) ...

That is Rhett's DIY (from e38.org) ...the same one I recommended as well. :D

The pics and instructions are so thorough that DIY is great for seat removal, seat cover removal, understanding how the auto seat belt adjustment wire works and hooks up...which have nothing to do with the subject of installing heated seats...but gets covered due to those things needing to be removed to get to the heat pads.

Lesson learned here is...if you can't find a DIY for a specific job...look at DIYs that may be related or similar...especially if what you are looking to do needs to be removed in that other DIY. :)

Flug540
04-15-2012, 08:04 AM
This is my understanding: this whole thing about pass seat occupancy sensor is to prevent injury to a child < 40 lbs in a car seat placed in the FRONT seat.

I believe that's correct.

Come to think of it, to simulate an adult occupied seat, I think you'd only need a resistor about 90K or so between the two wires, no diode. Because all the pad is is a series of parallel to each other switches parallel to the diode.

Flug540
04-15-2012, 08:06 AM
That is Rhett's DIY (from e38.org) ...the same one I recommended as well. :D

I know :) I just thought I'd provide a direct link.

dalekressin
04-15-2012, 08:10 AM
My Dog Sentinel ....... often rides shotgun.
Good thread about a minimum value sensor.
7G force decelleration set off the airbags.
Some airbags deploy on track with unfortunate consequences.