Red Flash

Hi All

So, I have heard, I believe, of two cases of spontaneous (or perhaps better said unwarranted) airbag deployments. The details I ****think**** were given by:

928 GT R - Passenger side deployment only on a 90 GT
Greg Brown - A customer had a deployment (don't remember which side, maybe both?) also on a 90 GT after the airbag light had been on for a while

I have not had such an event occur but I would be interested in hearing the details, if anybody else has had this happen or has heard of a case. If you post an event you have had or heard about, any details about the model year, situation (car already been an accident, warning light on, steering wheel replaced, etc.) would be interesting.

Thanks in advance, if any of you have any information to share on this topic.

Cheers, John

The Forgotten On

The 1990 model year was the first year for airbags and has a fair few issues. They were resolved in 1991.

The fix is to install the 1991 computer and harness. It's plug and play basically. Just make sure you leave the battery disconnected for a while before you touch anything.

Red Flash

Blake, interesting, thanks. Do you have any idea what these issues were?

docmirror

The early airbags, sometimes called 'series 1' used a quorum of sensors to initiate bag deployment. If only one bag went off, that was not a quorum sensor issue, it was a ignition pill problem. If the controller meets the quorum timing it's going to set off both bags. There is a resistance spec for the sensors that can have trouble, which is likely why the airbag light was on. There are also specs for the ignition pill. Another issue that can come up is a stray voltage that gets into the circuit of the ignition pill. By series 2 of the airbag controller, and sensors, there was a most robust insulation of the airbag circuits. I think it came during the mid-production of 1991 for the 928.

Please note, that removal of the airbag controller, is not a trivial thing. There are anti-tamper screws holding it in, and the wiring loom is pretty tight. To be completely sure, the bags should be changed as well, but the ignition pill will fire with the new controller to the older style bags. If the airbags are removed, disconnect the battery, and wait 15 mins before working on them. Set them on the ground, with the bag facing up, and the frame facing down.

Rob Edwards

Greg has commented in the past on having worked on numerous '90 cars with problematic airbag systems because the black box, the harness, and the sensors are all 1 big component in 1990, and to replace it all with the 91+ setup is something on the order of $5-6K.

Post 23: https://rennlist.com/forums/928-foru...ml#post7384164

worf928

‘91 airbag controller - integral with the harness (single part) - has the same parts number on the controller as the ‘90. PET shows change to ‘plugable’ harness and controller as ‘92+ with two part numbers. According to PET only the d-side airbag pill changed ‘90->’91.

If there is a controller change ‘90->’91 why the same part number?

Rob Edwards

Because I was lazy and didn't do my due diligence on the parts succession. Will rectify that in a bit.

worf928

Or, a stealth firmware change traceable only by controller serial number?

Petza914

As an extra safety precaution, once a battery is disconnected, an easy way to bleed residual current is to operate anything that would still work with the ignition switched off, such as parking lights.

SteveG

'93 GTS: I had the 2 airbag ( text in the pod display that can be temporarily cnx with the stalk and the separate bulb light on the left side of pod) lights tripped; the bulb cannot be cnx other than with Hammer or Theos Diagnostic. Theos software identified the culprit as "right front sensor malfunction". Where is that located? Anybody have knowledge of why that would go off under civilized driving?

Theos Diagnostic was used to cnx the bulb warning (and the text). I drove it a couple of miles, turning full left and right turns with turn signal cancelling correctly; well past the time limit when the text message would have tripped again (if there was an issue) = no lights or text.

The reason I mention the turning is that I have a 996 steering wheel installed with clock spring that occasionally does some clicking in a full turn, but generally the signal cancels w/o issue. The bag actuator is separate connector, but is part of the clock spring. I don't see how they could interfere with each other, but don't know why the right front sensor is acting up either. No reason for it to do that, so I'm fishing.

I really like the 996 wheel, but I dislike the bag issues (if indeed caused by the wheel) and would go back to the original wheel. Anybody know about replacement bags?

Rob Edwards

Theo has a nice writeup showing pics of the passenger side crash sensor here:

http://jenniskens.livedsl.nl/Technic...8/MyTip869.htm

docmirror

Right front sensor is mounted near the top of the A pillar, behind the upper hinge, on the inside of the A pillar. Remove the right seat(unless you are under 85Lbs), lay on your back, with a high intensity light, look up and to your left for a small module that is held on the chassis with a tamper-proof screw(can be tightened but not removed). Once located, disconnect the batt, wait for 15 min. Follow the lead of that sensor to a tri-lead barrel connector. Separate the barrel connector, and clean the leads with De-Ox-It or your favorite brand of contact cleaner. At this time, you can measure the resistance of the sensor, and then re-plug the barrel connector, and then reset your airbag fault with the hammer.

If it comes back, you likely have a sensor that is outside of the resistance spec(10 ohms I believe?) and will need to be replaced. Replacement is not a trivial job. The anti-tamper screw is a be-otch to get out and usually requires work with a small die grinder to cut off. It is a 6mm fine thread hole in the A pillar and the new screw doesn't need to be anti-tamper, but a normal 10mm head 6mm thread screw. Just make SURE the orientation of the sensor is exactly the same as the one that was removed.

Taguid

My airbag light would come occasionally when hitting bumps. I disconnected the barrel connectors at both a-pillar sensors and deoxited both ends. I have not had anymore MILs since doing the cleanup on the connectors for about 3 years now.

GregBBRD

There are plenty of things to watch out for and to be concerned about on a 928.

Fortunately, random air bag deployments are uncommon enough, that it is one of the things we (928 owners) don't have to worry about.

That being said, never just ignore airbag warning lights, especially if your car is a 1990 model! I've never heard of a random triggering event (on a 928) that did not have a warning light on prior to the deployment.

Red Flash

Based on the lack of responses describing actual occurrences known about to the community, this type of event sounds very rare indeed. I had heard of the above 2 incidents and was simply trying to find out, how common this is or if it actually ever happens.

Greg, thanks for that bit of background experience. I know these systems are well engineered and do constant self-monitoring. So, the main thing seems to be then to not drive the car, if the airbag light goes on, and to just tend to it ASAP, if it does go on.

Doing a trade-off, it sounds like generally the controllers in the 90s fail less often (i.e. need replacement or fixing), but the detachable harness on the 91s lead to a system that is a bit easier to work on. So, it would be interesting to know, when the type 2 systems that Docmirror was talking about (thanks Doc!) became available, and this could correspond to some kind of change in the 91 model year.

So, if Rob happens to see in PET why both 90 and 91 now have the same number, I would also be curious to know the answer too. Maybe the old 90 controller just became NLA and the 91+ controller superceded it?