Seatbelt pretensioner thoughts on a bypass

[IndianaRoadster]

I believe that if you only have stock seat belts you can still submarine. You would need a 5 point harness to prevent submarining.

If I understand it right, and I might not, but European cars didn't have them because they had seatbelt laws. If that is the case, then they must think that they weren't necessary as long as seatbelts we're used.

[cyberman]

Just to finish this up: I'd measured 0.5 ohm at the pretensioner, several times. That's under spec where it should be between 2 and 3 ohms. Today the weather broke so I got the seat unbolted and tilted on the side board so I could access the wiring harness. I pulled the connector apart (it's the roundish, bright-colored yellow/orange one) and could not measure at the pins as they were too small. So I cut the harness below the connector and measured 2.6 ohms which is in spec.

I can only theorize now that there is/was an intermittent fault in the pretensioner or the wire that runs from it to the connector under the seat. I believe this since I'd repeatedly cleared the code and it kept coming back after a few miles of driving. The seat was reupholstered last fall and perhaps the wire was routed incorrectly and got pinched. Or, the last thing I recall the day before the first time I noticed the light was that my phone slipped out of my jacket pocket and hit the pretensioner. Perhaps the impact knocked something loose.

In any event, I soldered in my 2.2 ohm resister across the two wire harness and left the connector unplugged. I took it for a drive and the light didn't come on. So, it's inconclusive, but if I were to do anything now it would be purchase both a new pretensioner and the wire connecting it to the harness. If I were to do anything...

[z3forlife]

You may be better off measuring voltage than resistance. Some circuits will measure differently when energized. I’d also check the harness end at the tensioner as well as the other end.

[cyberman]

You may be better off measuring voltage than resistance. Some circuits will measure differently when energized. I’d also check the harness end at the tensioner as well as the other end.

I checked it across the pretensioner terminals (and it read low). I have no spec on the other side, so I don't know whether it's voltage (and how much?) and I don't want to do anything with that circuit energized if it's connected. I think that I "cured" the code by disconnecting the pretensioner and bridging the wires with the resister proves that either the harness between the connector under the seat and the pretensioner or the pretensioner itself was having an intermittent fault. Now watch, the next time I take her out the light will come back on...

[nevan]

...Quick unplug/replug usually does the trick...

Luckily, this is how I've been able to get by (in conjunction w/ INPA SRS reset) with mine also.

To OP's point, here is an interesting YT link I've come across a while back. https://www.youtube.com/watch?v=UCz0w1vmEBw (1:15) - Btw, I'm not making any suggesting here.
The Youtuber uses a resistor with a diode (which makes sense. Also note that it's for e46. And I'm not sure if different chassis would be any indifferent).

[cyberman]

Luckily, this is how I've been able to get by (in conjunction w/ INPA SRS reset) with mine also.

That video is about the passenger seat occupancy sensor bypass. I got one off of ebay until I realized the module was just "lazy" and took about three minutes to turn off the light.

The current issue is the code for the pretensioner and I think I convinced myself a new pretensioner and it's wire is the only way to go for a proper fix. But at least for now the light isn't on and the bags will inflate in an accident.

[raldrich]

I'd like to know how to bypass it as well - but for a different reason. I'm trying to diagnose the issue I'm having. I got an airbag light and checked the code and it said "driver's side pretensioner fault". I looked it up and the resistance should be 0.5 - 1.0 ohms (and that is what mine was measuring). Thinking it was dirty contacts, I used some electronic part cleaner and a touch of dielectric grease to seal the connector and reset the airbag fault. Seemed fine.... for about 30 miles. Then, did the same thing. I had a spare pretensioner from an old seat and had it installed and the light went off - again. Same code. The likelihood that two (both used) pretensioners failed within 2 weeks is unlikely, but the local shop is likely to tell me that now I need to buy a new one. I'm willing to do that if that is really the problem, but they love to solve every problem by requiring new parts and then acting surprised when the problem persists. In the mean time, with the airbag light on, every time I drive the car, I risk injury because the airbag system (as I understand) will not activate at all when that light is on (a rather stupid design, if you ask me). So, with a temporary bypass, I'd like to clear the code and see if that solves the fault problem. If I can drive it that way for a month or so, I will be sure that it is the pretensioner and then spend the money to replace it. But if it is a wire fault or a wiring harness fault, then I can try to fix that instead. So, the question remains..... how can I (temporarily) bypass the pretensioner?? I'm a very large man and the seat belt is already quite tight when I cram myself into this car. That pretensioner is not going to keep me from submarining - physics will already prevent that from happening. Thanks!! Oh... BTW, I have a 2000 Z3 2.3 Roadster (non-M).

[cyberman]

My apologies - I usually follow up and complain when others don't. So, yes, the bypass is working fine. I too measured about the same ohm range as you did so I concluded that it must be an intermittent fault in the pretensioner circuitry.

I've seen seat belt extenders and even tried one off Amazon, but they didn't fit so I'd have to do more searching.

How to: I just traced the wires that went to the pretensioner itself, cut them and bridged the two going back to the computer/harness with the 2.2 Ohm resister. No light since and it's been months.

[Tallyho322]

My apologies - I usually follow up and complain when others don't. So, yes, the bypass is working fine. I too measured about the same ohm range as you did so I concluded that it must be an intermittent fault in the pretensioner circuitry.

I've seen seat belt extenders and even tried one off Amazon, but they didn't fit so I'd have to do more searching.

How to: I just traced the wires that went to the pretensioner itself, cut them and bridged the two going back to the computer/harness with the 2.2 Ohm resister. No light since and it's been months.

But do the airbags work?

I have been fighting the same issue, and eventually the fault locks up my airbag module and it can’t be reset easily (had to send if to Abel for his magic). But the light came on again after a year and the module is locked up again.

I don’t want to disable the airbags, but I am interested in a more permanent fix to this nagging problem.

Greg

[cyberman]

But do the airbags work?

I believe they will work, as long as the SRS light isn't on. After six months, the ohm bridge is still keeping the light off. Obviously, I won't have the explosive charge go off to tighten the belt a little more in the event of an accident, but I'll take that risk. When I was a kid, there weren't any seatbelts and when I got my first car in 1971 we had seatbelts, I think. But we certainly didn't have airbags and pretensioners, so my perspective may be different than that of other generations.