Seatbelt pretensioner thoughts on a bypass

[cyberman]

INPA shows a problem with the driver's side pretensioner (code 3 for my early 96). I have the seat out as I'm working on refurbishing the pedal assemblies. And I understand:

1) Usually cleaning the connector contacts fixes the issue and, if that doesn't work
2) Fixing broken delicate wires fixes the issue.

But I did some research on bypassing it and tricking the module if the above doesn't work. So, that brings up the whole question of how it works. Since it has only two wires, I'm thinking the SRS module measures resistance across them and if it's an open circuit it reports a problem. I may want to bypass it since the cost is north of $250 now for my 96.

So, that brings up the question of what is the resistance for an undamaged (good) pretensioner and how to test it. I can't find much, one video, not Z3-specific, says it should be around 0.5 ohms and the device is from a BMW.

Mine measures about that right at the pins where the funny plug goes into the pretensioner. But that's a lot of assumptions. Numerous posts say to bypass with a 2.2 ohm resistor, but that also applies to the airbag(s) themselves.

Any thoughts on this? Yes, I know for safety reasons some of you will advise not to bypass it. Other than that???

[TexaZ3]

I would not bypass is, simply because I want a functional system.
Wiring and/or connectors are usually the problem.

[cyberman]

I would not bypass is, simply because I want a functional system.
Wiring and/or connectors are usually the problem.

Yes, I know for safety reasons some of you will advise not to bypass it. Other than that???

[Wcumoron]

Safety restore.com does pretensioners and seatbelt rebuilds after accidents, do know why they wouldn't be able to fix the functionality of a non blown unit.

Not affiliated in any way, was gonna be my last resort to turn my light off for the passenger pretensioner.

[White Z]

Let me know if it works? I called them but they wouldn't do mine.
I reached out to, "Myairbags.com" and they said they could repair it. It's not high on my list currently. Been driving the car with a piece of black duct tape over the light for a couple of years now. I've got to the point that I don't even notice it anymore. That's bad.

[zellamay]

Yes, I know for safety reasons some of you will advise not to bypass it. Other than that???

"Other than that???" Yes. If you get in an accident in which you are hurt, and the insurance company discovers any bypass, they may not pay your expenses.

[khammack]

Yes, I know for safety reasons some of you will advise not to bypass it. Other than that???

Really? You need another reason?

[s8ilver]

So it greatly reduces your chance of hospitalization or death, but doesn't guarantee you won't get hurt if you use it? Hmm, where have I heard this debate before? I can't quite put my finger on it.

Roll hoops. I think it was roll hoops.

1996-BMW-Z3-1.9-4USCH7321TLB67110_1_mGed7K.jpg

[Hoyt Clagwell]

So it greatly reduces your chance of hospitalization or death, but doesn't guarantee you won't get hurt if you use it? Hmm, where have I heard this debate before? I can't quite put my finger on it.

Roll hoops. I think it was roll hoops.

Yeah that's right, roll hoops but I think you need 3 of them.

[cyberman]

It's moot, I measured about 0.5 Ohms at the connector that plugs into the car harness sprayed it with deoxit, cleared the code and it didn't come back during a short test.

I have no data on how much that pretensioner helps (reduces death or injury), but I doubt it's that effective. And face it, after 25 years parts are drying up and getting ridiculously expensive.

But rather than a moral judgement, I was looking for data on how much resistance should there be so we can all know how to test it. It is useful to test components rather than just replace them.

[z3forlife]

Any time I move my driver seat forward or back it sets my fault for the tensioner. Quick unplug/replug usually does the trick. Unless there’s harness damage it’s rare for one to actually fail.

[cyberman]

Any time I move my driver seat forward or back it sets my fault for the tensioner. Quick unplug/replug usually does the trick. Unless there’s harness damage it’s rare for one to actually fail.

Thanks, I'll try that, assuming I can reach it without removing the seat. If I can get to the connector topside on the other side I'll measure the resistance there. It might be an internal break in one of the wires. So, am I correct in assuming if the airbag light is on the bags are disabled?

BTW: I remember the first time I encountered a seatbelt, before that, there was a risk of being ejected. Then came the crash bumpers and other safety things such as airbags. Maybe I'm a risk taker, but I've already removed the submarine prevention plates on both sides. I understand European versions didn't come equipped with them. Frankly, while I cringe when I see bikers without helmets, well that's there right. But I fear for this country, and what I call the chicken-ization of our culture where there are huge over-reactions to minor (in terms of probability) product safety issues.

Bottom line, if I can get the airbag light off and have functioning airbags, screw the pre-tensioner. My seatbelt is always too tight. So I looked up the effectiveness of pretensioners. According to the NHTSA:

A belted driver or right-front passenger has an estimated 12.8 percent lower fatality risk if the belt is equipped with a pretensioner and a load limiter than if it is not equipped with either (95% confidence bounds: 2.6% to 23.0%).

I'll take my chances.

[IndianaRoadster]

"Maybe I'm a risk taker, but I've already removed the submarine prevention plates on both sides." [Quote]

At the time Europeans had seat belt laws and we didn't. BMW put those submarine prevention plates in to protect them from law suits. I took mine out because no one is going to ride in my car with out seat belts.

[zellamay]

I just gotta know: what is a submarine prevention plate? The only thing I can think of is that it keeps a Z3 from being transported in a submarine.

[z3forlife]

Thank a lawyer but ultimately the insurance companies are the driving force behind all the various “Nannie’s” life presents now compared to the 50s-70s.

[khammack]

I just gotta know: what is a submarine prevention plate? The only thing I can think of is that it keeps a Z3 from being transported in a submarine.

It is designed to (maybe) keep you from "submarining" under the dash in an accident. I think it is also called a knee bolster.

[s8ilver]

I just gotta know: what is a submarine prevention plate? The only thing I can think of is that it keeps a Z3 from being transported in a submarine.

Metal plate behind under panel and the 2lb weight in the glove box door (which is the main reason they sag). I left the driver's side plate in, but deleted the glove box door chunk. I'm solo 99% of the time, and NO ONE rides in my cars without a seat belt either. If they refuse, I'll point them to the bus stop. I just had my 36th medical appointment since my rear ending in 2019, and still have about as many to go. I was hit at relatively low speed too.

[BimmerBreaker]

You spent $10k on maintenance for your car. I'm surprised it even crossed your mind to skimp on a $250 item which is a critical safety component

I just gotta know: what is a submarine prevention plate? The only thing I can think of is that it keeps a Z3 from being transported in a submarine.

Early E36 compacts that came out of the Spartanburg facility came with a button to enable submersible mode. The US DOT stated that they did not believe US drivers could safely operate a submersible craft, so BMW had to disable that feature on all future cars coming out of Spartanburg. I've heard a few early '96 Z3's still had the submersible toggle function, but haven't seen any proof of such. Lotus Elises did not have to meet this safety requirement due to low production numbers, so Lotus Elises have a submersible toggle function

[zellamay]

You spent $10k on maintenance for your car. I'm surprised it even crossed your mind to skimp on a $250 item which is a critical safety component



Early E36 compacts that came out of the Spartanburg facility came with a button to enable submersible mode. The US DOT stated that they did not believe US drivers could safely operate a submersible craft, so BMW had to disable that feature on all future cars coming out of Spartanburg. I've heard a few early '96 Z3's still had the submersible toggle function, but haven't seen any proof of such. Lotus Elises did not have to meet this safety requirement due to low production numbers, so Lotus Elises have a submersible toggle function

I'm still laughing as I read this to my wife.

[cyberman]

You spent $10k on maintenance for your car. I'm surprised it even crossed your mind to skimp on a $250 item which is a critical safety component

I wish it were only $10k as I'm up to $15k now and still have another grand to go for a clutch job which I'm not doing myself on the floor of the garage. I'd happily accept a 12% great chance of death, but note that NTSA says that 12.8% includes having both a pretensioner and a load leveler. WTF is a load leveler and I doubt my car has one. So, the risk of dying in an accident are roughly 1 in 107. So, even if the 12.8% holds (which I doubt), then the risks of dying in an accident increase to 1 in 95 and IMO so what? Don't get into an accident if one is worried about it.

If safety restore can fix it for $75, what the hell, I'll send it in. But I'm still not sure if the thing is broken or if I have a wiring harness issue. There has got to be a way to test the resistance and determine if it is within limits or not, but nobody is giving me the information. So, I contacted safetyrestore.com and asked me the question. They gave me a link to this video:

Buckle pretensioners aren't covered but that 2-3 ohm spec is mentioned with a similar charge circuit.

So, I looked up those odds of dying. That's lifetime odds, so if you're old, well you've already used up a large portion of your lifetime so 1 in 107 probably changes to something like 1 in 200 or so. Then I found this list of odds of dying (all lifetime) and found I've got a better chance (or worse) of dying from a fall (1 in 106), gun assault (1 in 289), drowning (1 in 1,128). You can see the whole list here: https://injuryfacts.nsc.org/all-inju...odds-of-dying/

[BimmerBreaker]

So, I looked up those odds of dying. That's lifetime odds, so if you're old, well you've already used up a large portion of your lifetime so 1 in 107 probably changes to something like 1 in 200 or so. Then I found this list of odds of dying (all lifetime) and found I've got a better chance (or worse) of dying from a fall (1 in 106), gun assault (1 in 289), drowning (1 in 1,128). You can see the whole list here: https://injuryfacts.nsc.org/all-inju...odds-of-dying/

I think your logic may be backwards here. As you say, you've "already used up a large portion of your lifetime" so then it stands to reason that anything that poses a risk of death would be more risky to an older person; ie. your risk factor would increase not decrease. In this example 1 in 107 for the general population would be lets say 1 in 50 for someone of senior age and maybe 1 in 200 for someone of a younger age as the younger person has a lower chance of death

[s8ilver]

Don't get into an accident if one is worried about it.

Next time I'm rear ended while stationary I'll give that a shot.

[cyberman]

Oh yes, age is a factor and that's why the young and the old get blasted with higher insurance rates when they can least afford to pay them. But the risk is also a function of miles driven per year and mine is under 5,000/mpy. It's a function of gender so men are higher. It's a function of drinking and other drug usage and I don't use anything. It's a function of risk taking and I must admit I lean on the throttle a bit.

So many factors so little time to calculate it all. In the end, I'll take a working airbag and fastened seatbelts over a disabled airbag because the pretensioner is shot. But at least now I can use one of 100 2.2 Ohm resisters Amazon was kind enough to send for $5.99 (6 cents each) to test and see if the pretensioner is shot before sending it in for repair.

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[khammack]

I'm solo 99% of the time, and NO ONE rides in my cars without a seat belt either.

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

[s8ilver]

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

Good point. In Lemons our submarine belt has to be anchored to the car with a minimum 1/4"x6"x6" plate. We went further and tied that plate into roll bar reinforcement and car unibody. I'll study the geometry of my 5ft tall wife and run some numbers. She's the only other passenger, perhaps once or twice a year. She likes her new car way too much to probably ever ride in mine again anyways.

I do like our new track rule. Passenger seat has to have same restraint as driver's seat on open lap days. Instructors were getting scared of 5 point-belted novice drivers that were getting a bit too exuberant.

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