MikeT 90 C4sixer

So i finally got some time to tackle the infamous '90 air bag lites on and codes in the DERM. I have 3 codes, one for each sensor and the lite on code. So far all i have done is pull the battery and battery tray, so i could get to the LH sensor. It looks like i can get sensor off fairly easy. I was hoping the sensor lead would have the connector right there, so i could disconnect it easy and check the resistance to ground. But it looks like it goes thru a rugged rubber grommet, into the drivers compartment

Anyways, my question is do i have any risk of setting off this air bag in the steering column? My FSM says something about disabling the system, with a specific procedure. I figure with the battery fully removed, it should not be able to go off. Of course i will be careful with the sensor.
Thanks for any tips.

WVZR-1

The connector for the LH Sensor is easily accessed inside the car near the left side kick-panel. It's a barrel connector like early audio and the wire will be in a yellow sheath. Easily found. If you've got the FSM follow the procedures for SIR disable. Why would you be interested in "short cutting" the recommended procedure?

peyc2

FWIW some airbag systems can remain "charged" and can activate for up to a 1/2 hour after battery removal. I am not sure about the ones in your 90, but, in every class I have taken on extracation of trapped passengers we always assume the airbags to be a problem. I have seen many accidents when you would have thought the airbag would deploy, but they haven't, and if we have to get people out, we are always careful of working between the driver and the steering wheel, or passenger and dash board. We have a guide on our heavy rescue truck which we can check by car make, model and year for safe deactivation.

MikeT 90 C4sixer

Hmmm, inner kick panel, i guess i can pull the lower knee bolster, and look for the connector. The FSM isnt always correct, has mistakes in it. Also, sometimes the connectors arent where they say they are. Common sense tells me if the system is de-energized, it should not go off.
Anyone else with experience?

MikeT 90 C4sixer

So do you disconnect the BAT as one of the first things you do in accident? My bat will be disconnected for days before i pull the sensor.

peyc2

Follow this link, it talks about a chart to determine for the model "deactivation" time, it's usually up to an hour. Days, you should be fine.

You can also search for a video that I have seen, that shows a crew working to remove a victim, and after they have cut the roof off the car, then the driver airbag deploys and sends a fireman flying backwards. It pretty wild. Just be careful.



http://firstrespondertv.com/ronmoore...rbag%20ERG.pdf

MikeT 90 C4sixer

Well i decided to air on the side of caution, and disable the SIR system. Wasnt that bad, besides i am learning more and more about this '90 C4.
Tonight, got to the LH sensor connector, and checked resistance to ground, and it was less than 1ohm. Hmmmm, that is what the code was for. So anyways pulled the sensor off the frame, and started cleaning things up. Got a new tube of dielectric grease all lined up!
Lots of reading lately in service books.....

MikeT 90 C4sixer

So i got the left sensor all cleaned up and re-installed. Now working on the right side. Got all the business removed to access the sensor, but then i quit. My question is now, should I tear into the pass compartment, footwell to access the connector? Or not bother with it. I have not had any of that area pulled apart. My FSM is a little fuzzy on how to access the connector.
Thanks for any tips,
Mike

WVZR-1

The sensors are the same right to left so "knowing" the pigtail length will give you the general idea of where the connector is located. I don't believe there's anything on the right side that requires removal. The FSM image is I believe correct, just locate the yellow sheathed cable from the DERM and follow it to the right and the connector should be easily found I believe.

Streamline

I am wondering why you are going to the DERM module? My 90 had the light issue due to corrosion where the two sensors were located on the frame. I un-mounted each sensor, sanded the mounting area under it and applied the dielectric grease under the sensor and on the frame. I did not touch the orange Bosch DERM module. After that it was a pain to erase the stored code or codes. These codes are stored in the Body Control Computer (BCC) and not the ECM. In order to erase the codes a specific sequence and timing of grounding the data link connector pins is required to erase the stored codes on the BCC. Disconnecting the battry will not erase the BCC codes. I hope this helps.

MikeT 90 C4sixer

I know where the sensors are, as far as the right one, the connector is under the carpet/trim panel in the footwell. I was just wondering if there was some easy way to access it. After looking at my FSM, i am going after it tonight. I want to check the resistance from the ground term to chassis. Then pull the sensor off the frame and clean things up.

I have no intentions of going to the DERM box. no need to. After all done, i will be praying that this clears my 3 codes up, and turns off the 2 dash lites.

WVZR-1

The connector is just about directly behind the radio receiver box mount and if you just feel under the edge of the carpet (you do NOT need to pull it back) you should find the connector or the yellow sheathed cable from the DERM, follow that towards the right to the connector. Best I recall maybe 6 - 8 inches from the right hinge post/kick panel.

MikeT 90 C4sixer

Thanks, i found it no problem. I did pull the lower trim panel out, just so i can look at things easier. The sensor connector was NOT installed in its proper holder bracket. And the drivers side did not even have a holder bracket, at least i couldnt find it!
Checked the ground resistance, and it was less than 1ohm, but that prolly doesnt mean much. Pulled the sensor, some corrosion under it, but not too bad. Cleaned it all up, di-electric grease, and put most of it back togethor. Next hook up a few things under the dash, the battery, and hit the code reset! Wish me luck!

WVZR-1

GOOD LUCK!! The code clearing can be a damn nuisance - maybe the worst of the whole ordeal!!

bob guzzy

A good way to clear the codes is to use a push button starter switch or just a switch that returns to center.

Hook the ground on one side and plug the other into the correct Assembly line connector, and click away.

MikeT 90 C4sixer

Yea, i have a nice push button toggle switch all made up. wired 12" leads both the NC and NO contacts, so it should work fine. I just pray the reset clears the codes and lites, and they stay off!

MikeT 90 C4sixer

SUCCESS!!! Finally got it all bag together and did the code reset, and the lites are off!! Woohoo!! it did take me 2 attempts to reset, with the 3sec on/off trick. I think i was late on the 2nd 3 sec part....But anyways, a big relief. these 2 lites have been on since i have owned the car. Previous owner didnt do anything with it. All i have left to do is put the drivers side lower trim panel up in, when i get a chance. After all, it was alot of work just to do one little thing, but at least i learned some things about my car.
Mike

WVZR-1

That's always good to hear when someone returns and either wants to celebrate the success or explains maybe why the project wasn't a success.

Your success in just a couple attempts is fortunate - some certainly struggle. You've demonstrated that it can be done IF the components are all "good". Diagnostics are key!

MikeT 90 C4sixer

Thanks ZR1, but i did do my homework on this one. did alot of searching, reading up on the solutions, and the service bulletin. The internet is such a good thing, as well as these forums. My FSM was invaluable, i read that alot. And i took my time with this job. Originally, earlier in the summer, and shortly after i got the car, and found out about these lites on, i wanted to fix it right away. Apparently, they did not have to be cleared for it to pass inspection, so i bought the car this way.
But this car had(has) so many other problems, i had to focus on more important things. Still have not driven car, or put up the lower drivers trim panel. I had some recent medical problems, so my driving days are limited. Soon i can get her out and back on the road.