Air bag light!

[CurlyBen]

Hi all

I've been lurking around here for a while as I get the job of fixing my family's cars which until recently included two Z3s! (One has now been sold). Unfortunately I've got a problem which I can't find covered on here before.

The airbag light's been on for a while so I bought a Creator C110 code scanner, which brought up 3 fault codes. After clearing the codes one is repeatedly coming back (within seconds of the codes being cleared): "18 - seat belt lock, driver". Everything I can find online suggests that this is a fault with a sensor in the seat belt socket - however on this car (1.9 Roadster, built October 1998) that sensor doesn't exist! The only electrical connections to the seat are the power for the position motors, an unused connector for heated seats and the seat belt pre-tensioner connection. I've disconnected the pre-tensioner connection which throws up a different error which can be cleared once it's reconnected. There's no code corresponding to the passenger seat.

I think it's unrelated, but the airbag light came on either when the car was taken for it's last MOT or just after (my mum thinks it was on when the car was returned from the MOT, my dad thinks it was just after). Some work was carried out at the last MOT but everything was mechanical (exhuast/brake flexi pipes I think).

Has anyone else seen this issue or any ideas what might be causing it?

Cheers!

Ben

[Robert T]

Hi and welcome to the forum.

I'm afarid don't trust the code table you are using for you scanner. The UK spec Z3 (and I think Euro spec as well) do not have a switch in the seatbelt buckle - this was only fitted to US cars for the dashboard seatbelt light - on the UK model this works on a simple timer.

The usual problem with the airbag light coming on is due to poorly designed connectors under the seats, which can cause a momentary break in the circuit, typically when the seat position is moved. The light latches on and has to be reset with a tool.

As you have cleared the codes and the light comes back on, then you have a persistent fault. You need to check the following:

* Check the wiring under both seats for damage
* Ensure that the contacts in the connectors are clean and free of moisture - use WD40 or contact cleaner
* If your car has a passenger airbag, then check the passenger seat occupancy sensor

I have worked on one Z3 which logged codes for driver's pre-tensioner and passenger occupancy sensor, both of which were due to water ingress. If you have the seats out, check under the carpet as there is several inches of foam under the seats, so even if the surface of the carpets feels dry, there can be a lot of water trapped in the foam. The driver's side fixes with WD40, the passenger side needed an occupancy sensor bypass installing (or a replacement mat).

Although I have never seen it on here, it is also possible that a fault with the airbag(s) or control module is bringing the light on.

Cheers R.

[g8jka]

Although I have never seen it on here, it is also possible that a fault with the airbag(s) or control module is bringing the light on.

When I bought my zed the airbag light was on and it was the control module that was shot. Took me months to find a second hand control unit which had to come from Germany but once it was replaced the light went straight out after a reset.

[BonBon]

Try removing the yellow connector (two contacts inside connector) under the seat and spraying with contact cleaner - works for me and often need to do it a couple of times before getting a good contact.

[spurs fan in a coupe]

Lots of into here

http://www.zroadster.net/forum/viewtopi ... 8&p=382016

[CurlyBen]

Thanks all for the replies.

I was a bit sceptical at first about whether the code table was correct, but it correctly identifies the pre-tensioner codes when they are disconnected (and they clear fine when reconnected). Code 18 doesn't make any more sense interpreted against any of the other BMW airbag fault code lists I've found.

I'll pull the passenger seat out tomorrow and have a look for any additional wiring under there, but the code specifically relates to the driver's side. Is there any obvious way to check whether there is a passenger airbag? (Which doesn't involve setting the airbags off!!). I've had the driver's seat out already and there's nothing wrong there.

g8jka, when you replaced the ECU did you have to get it recoded? I've seen some on eBay fairly cheap (haven't checked yet they are the correct modules, but are being advertised as Z3 airbag ECUs) and I'm wondering about swapping one out, but that obviously won't help if it needs recoding (which I don't have the facilities to do). The code does look a little as though the ECU is confused about what sensors it has installed. Having said that, I did manage to turn it off for a few minutes today (normally it's back on in seconds) but as I did nothing differently I don't know why!

Robert, you mentioned checking under the carpet as there's thick foam - do you mean under the cloth of the seat, or are there sensors below the carpet on the floor?

Cheers

Ben

[g8jka]

No Ben, it didn't need recoding it just plugged straight in. There was hundreds on eBay when I was after one, but none with my part number which seemed to be scarce. Just make sure you match the part numbers and it should be plug and play. You have to remove the centre console to get to the module though as it's located under the heater controls. May be worth a try if you think it's not working properly as if it's one of the more common units you can pick them up cheap. Then you will just need to rescan the module.

[Robert T]

I meant underneath the carpet on the floor of the car. If this is wet the it will make the connectors (and everything else) wet. On later cars there are sensors under the carpet, but not on pre-facelift cars. If there is water under the carpet, this is a good indication that the seat has probably been wet at some point as well and this is what would damage the seat occupancy mat. Definitely worth a check whilst you have the seats out.

Very easy way to check for a passenger airbag - the word "Airbag" will be stamped into the trim in the indentation on the passenger side that corresponds to the driver's instrument binnacle.

Cheers R.

[CurlyBen]

Thanks guys, I'll check the passenger seat tomorrow then and if that doesn't help I'll look at swapping out the airbag ECU. I do know the window on the passenger side has been leaking!

Cheers

Ben

[CurlyBen]

Just as a quick follow up, I fitted a bypass to the passenger seat occupation sensor and that seems to have cured the problem, so the text the code reader was reporting didn't match up with the fault. Still, at least it's sorted!

Cheers

Ben

[mjguk]

Thank you so much for this thread Ben. This has been such a help. I have been looking for the past week or so for a fix for error code 18 Seat Belt Lock - Driver - I've tried everything that has been listed on various threads to no avail. Today I saw your latest post saying that it was the passenger seat pad - So I've nabbed a friends by pass sensor and what do you know my light is off and out for good.

Thanks for posting

C110 Error Code 18 Seat Belt Lock - Drivers side is Passenger Seat Pad which is easily rectified by bypass sensor.