WallyP

We are seeing some problems with "Air Bag Malfunction" warnings, so I am starting a study on the system.

I would appreciate any input on solutions that you have found for these problems.

SeanR

Did you check the connection on the main control unit? Is this the car that was at SITM?

Herman K

I had an airbag warning light come on for the longest time. I read through about every thread I could find and checked accordingly and still could not eliminate the problem. The hammer wouldn't identify the presence of the airbag system and this let me to believe that the main control unit was defective, indeed after sourcing one of these unit on e-bay (as you may know is a 944 part #944.618.217.02) I have put this issue to rest some 3 years ago. I recall that while trying to source a unit I found an outfit in Dallas that repairs airbag controllers at a reasonable cost and perhaps one of these days I may still have the old unit fixed in order to have a spare. I just went throught the same experience with an ABS/differential warning light that would come on any time I hit a road bump by changing out the CWS controller that fault has been corrected. Good luck with the research hopefully my input helps some one with a similar problem.

928 at last

Hey Wally,
Fixed mine last year through reading in the forum here. Really couldn't believe that a connection that clean could be "defective", BUT, after using DeOxit on the right (Passenger side) crash sensor connector, Q-tipping it off (Twice for luck) and applying the "Gold" for insurance, the error disappeared. These things are incredibly sensitive to any contamination. I swear, mine looked new when I pulled the connectorapart, and the residue on the Q-Tips was non-existent. my system showed a problem on a computer diagnostic connection though which identified the right (passenger side) crash sensor as the problem. Had some issues finding DeOxit in Canada, but did eventually, and the stuff really works.
Best,
Rob.

Nicole

Where exactly is that connector located?

derporsche928

Thanks for starting this thread Wally....
As you know mine has an "Airbag Malfunction" alarm after I start the car, and I clear it with the stalk, and it comes back on every half hour or so as I'm driving it..... Dave Chamberlain reset it last year after I'd replaced the passenger side pill, (my research had indicated it was the most common failure point) and it stayed good for all of 2 hours, and then came back to do the same as described above..... I then changed the drivers side pill, and (as you know, again...) the Hammer saw the fault as "Control Unit Faulty." As we had discussed, this could mean that the unit is faulty, or perhaps it could be a connectivity issue..... Of course, you reset it, but it came right back to the aforementioned fault symptoms..... David had a spare, and sadly, it is not plug and play, as the wiring comes directly from the unit to each of the system component connectors...... David said it may be sold, but he told me to call him next week, and if it's not, he'll send it to me to see if when I install it, it fixes the problem..... I'd also be curious to know if there would be a way to jumper the Control Unit to essentially see all of the separate components as good to make the fault go away..... (Kinda like jumpering around the tire air pressure monitoring.....) Need to look at the wiring diagram, and see if I can make sense of it, though I'd venture to say this would not be an easy task considering my limited expertise with the Porsche wiring diagrams.....
I'll be watching this thread, but let me know if you come up with anything significant......
In the mean time, I'm going to find some DeOxit as Rob had mentioned above (or whatever you told me.... I wrote it down....) and try cleaning all of the connectors, and see if it will reset.....

Nicole,
The passenger side crash sensor (pill) is located above the LH and EZK boxes..... It's a black plastic module about 1" square x 2" long with a metal base held to the car with nuts that are serrated.... It takes a special socket to remove them, but vice grips would probably work..... The drivers side pill is in a similar location, up above the abs brain...... The pills have a 1' pigtail coming from them with a connector that looks like the oxygen sensor connector.... This connector plugs into the control unit wiring connector, and is held by plastic clip that is only a few inches from the actual sensor.....

Best,

Nicole

Thanks, Greg! I had a fault some time ago that indicated it came from the right crash sensor - but of course it was not clear whether that was a wiring or sensor issue. That fault has been cleared and did not come back since.

Also, every now and then, when I hit a hard bump, I get the airbag warning for a few seconds (display AND warning light), and then it goes away. This never stores any fault codes in the system. I'm not sure, if it is an actual warning, or the instrument cluster briefly goes crazy from the bump.

Since it is rare and never lasts more than a few seconds, I'm not stressing about it - but it is a bit annoying when it happens. If there was a relatively easy solution, I would love to have it fixed.

EMan 928

This is exactly what is happening to my car...I hit a bump or expansion joint in the road and the both display and warning light comes on. Both clear by themselves after a few seconds if another bump doesn't come along. I also hear a clicking noise somewhere under the dash or behind the center console. Happens everytime I drive it so would love to get this one fixed.

Ed Scherer

Regarding the connection to the crash sensors, see "Fixing a nuisance air bag system fault 3129/3229". It includes photos (that I have also reproduced below) showing the crash sensors and the associated connectors that can be disconnected and cleaned.

Other related threads:

• Air bag fault warning
• Air bag sensor removed - any way to test it?
• Pass. Airbag sensor removed-can I test it?
• '91 GT Pass. Airbag sensor UPDATE
• Airbag warning light
• Help! 1990 Wiring Diagram - Right front crash sensor
• Color of Air Bag Control unit in a '90

You'll notice a very strong theme in those threads: that (IIRC) every single air bag fault that has been tackled (that I know of that has been discussed on Rennlist 928) has been solved by cleaning the connectors with DeoxIT (or similar cleaner/deoxidizer). Thanks go to docmirror for confirming my suspicions about resistance at these connectors when I solved the problem on my car back 4 years ago. And, for the record, this problem has never returned on my car.


For the record (and future thread-searchers), here are some photos that help locate the left side crash sensor and related connector (hiding behind the bracket):





... and the right side crash sensor and related connector:

EMan 928

Ed,

Thanks so much for the resources! I just ordered a bottle of DeOxIT and hope to follow your advice over the weekend. One question, when you clean the contacts what are you using? Just the DeOXit, or do you rough them up with a little sandpaper or something.

Ed Scherer

Just the DeoxIT; plugging/unplugging a few times after applying DeoxIT should do it, unless you actually see visible crud that needs to be cleaned off. A little light sanding (or rubbing with an eraser) first probably wouldn't hurt.

FWIW, I always keep a little bottle of 100% DeoxIT (D100L-25C, with the needle dispenser) around and use it on various electrical connections on my car. Good stuff. DeoxIT comes in lots of varieties.

Ed Scherer

This, to me, sounds more like an intermittent signal disconnect to the instrument cluster rather than the crash sensor connector problems, the tip-off being that the fault isn't stored and that the condition clears right away.

Looking at the Instrument Cluster electrical diagram for the '90 S4, I see that the air bag fault signal passes to the instrument cluster on plug 3 pin 11 (GN/YE wire from pin 6 of connector T52 for the air bag control unit; see upper-right hand part of Air Bag etc. diagram for the '90 S4). It might be worth reseating and DeoxIT-ing those connections.

EMan 928

Hi Ed,

Is it hard to remove the instrument cluster to check? I'm on the beginning of the learning curve with these cars.

Ed Scherer

Never done mine (need to sometime, though, to fix a lighting issue), but here are a few threads that cover the issue for various model years:

• 15 minute instrument pod removal update and instrument light bulbs for an OK price
• Pod Removal and Instrument Cluster Repair w/pics (Part I)
• Pod Removal and Troubleshooting (on an '85 928)

Gary Knox

I've used Shocki's 15 minute pod removal, and it works great on my '94. As an "advisory", however, the steering wheel hub on my car is extended about 1", giving a significant increase in maneuvering room for the pod. I disconnect the battery for a full 24 hours before removing the wheel/airbag if I do it that way.
Previously, I've always removed the steering wheel on my S4's (no airbag).
Gary Knox