Airbag light won't go off

[Nybbles2Bytes]

In my 1998 328i my scanner shows no codes in the airbag module but it does show the status of a few items. This is what it shows:

Seat belt buckle switch, driver - disconnected
Seat belt buckle switch, passenger - disconnected
Seat passenger occupied - Yes

So it seems to think there is someone in the passenger seat all the time but no one is actually in it and there are no error codes.

Does anyone know what the likely culprit would be and perhaps a reasonably smart series of steps to diagnose this problem?

I almost forgot, I tried buckling the passenger seat belt thinking if it thought the belt was fastened it would turn off but that didn't help.

Thanks,
Reg

[Eric93se]

The small connector under the seat for the buckle is probably corroded. You can use deoxit 5% and the small bristles of a toothbrush to scrub the inside of the connectors.

[bluptgm3]

....then clear the codes.


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[MParallel]

....then clear the codes.


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my scanner shows no codes

Oh well...

[gc325is]

I recall..... The passenger seat sensor pad is known to fail, breaks in the contacts. The seat belt connected, detector were also known to have problems. If the system detects these failures, the air bag deployment will err on the safe side and assume no seat belts and a passenger is present and deploy as such.

[bluptgm3]

In my 1998 328i my scanner shows no codes in the airbag module but it does show the status of a few items.

This is what it shows:

Seat belt buckle switch, driver - disconnected
Seat belt buckle switch, passenger - disconnected
Seat passenger occupied - Yes

What scanner are you using?


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[Nybbles2Bytes]

What scanner are you using?

Foxwell NT510

[bluptgm3]

Here is what I have found for the Foxwell NT510.

When it comes to system diagnostics the FOXWELL NT510 supports all 10 OBD2 test modes. It also scans all the main OBD1 systems of a BMW car. That means you can read and clear codes in the ECU (engine), ABS, SRS, transmission, and SAS. NT510 is able to troubleshoot all BMW problems.

So check the seat belt latch sensor / occupant sensor connections and clean them, as indicated above. If the codes return then the errors have to be corrected, I.e., components replaced.


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[jclausen]

You need to scan the Car with a good shop quality scanner I guarantee there are faults in the air bag control unit

[Nybbles2Bytes]

So check the seat belt latch sensor / occupant sensor connections and clean them, as indicated above. If the codes return...

As I said at the beginning, there are no error codes so there is nothing for my scanner to do. However, I did just power probe the wires right at the control module and the seat belt sensor is certainly sending a signal of whether the seat belt is latched or not. The occupancy sensor is sending a signal but it doesn't change based on whether a person is sitting on the seat or not. It sends out a 9.1V signal with a quick down pulse to 1.5V briefly about 2 times a second. Unfortunately I have no idea what that means and my scanner doesn't pick up the occupancy sensor information.

My understanding is that the sensor mat goes through an air bag seat sensor control unit so theoretically it could be the sensor or that unit and I have no way of knowing which. I guess could buy both and then send the part back that I don't need although I don't like doing that sort of thing but while my car is in pieces it would be prudent to have both possible likely points of failure on hand. On the other hand, I've read that those sensors to do go but never read anyone saying that control unit went bad so I'm inclined to just get the sensor.

I did have that seat out a few months ago for another reason and I didn't notice any issues with corroded terminals so I'm inclined to think that won't be a problem but it's certainly a good quick free (other than my time) step to do first so thanks for the suggestion.

[MParallel]

Passenger occupancy control box is under the seat.

Many have a mod that just tells the module, the seat is permanently occupied, when their mat is broken.

[bluptgm3]

E36 passenger seat occupant sensor simulator


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[Nybbles2Bytes]

Well, I ended up buying a new seat pad sensor array and took the seat out, pulled up the seat padding to get the sensor, found out that the sensor I bought was the wrong one as it had a completely different configuration, put it all back together and the warning light went away. I guess there was some bad electrical connection that got fixed just by pulling the seat out, working on it a little and putting it back together.

I'll take a bit of dumb luck as a win any day!

[JDStrickland]

Well, I ended up buying a new seat pad sensor array and took the seat out, pulled up the seat padding to get the sensor, found out that the sensor I bought was the wrong one as it had a completely different configuration, put it all back together and the warning light went away. I guess there was some bad electrical connection that got fixed just by pulling the seat out, working on it a little and putting it back together.

I'll take a bit of dumb luck as a win any day!

That's a Good news, Bad news story. The good news is, it works. The bad news is, you don't know why.