How to pull airbag light codes?

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Blue Turd

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So I took the clock spring out to test it on the bench. Turns out it is fine. The shorting out I reported earlier was actually what was supposed to happen when it is unplugged. In the plug end if it is not plugged in it shorts the pins, in the event the plug is ever unplugged it disables the system and throws the air bag light. I just replaced the part anyways, as I had the new part in hand and the steering wheel was already off.

After that didn't fix it (expected at this point), I took the truck to my local place as their diagnosis guy was back in town. The tech was not able to even communicate with the airbag unit (with a legit GM tech2 scanner or the fancy Snap-on unit). He says in his experience with these systems that means the air bag computer is dead. Its very likely the internal capacitors have oozed out and thats the end of that. This also means my scanner still might be able to pull codes, but obviously couldn't as the module was dead.

These modules are fairly easy to find on ebay or in a junk yard, so I will order one and see what happens after that.
 

Blue Turd

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I ordered what is supposedly a tested good working used unit (OEM). $5.50 shipped to my door. I cannot believe how cheap that is. Tons of them on ebay for around that price. My old module didn't look bad in the inside (no catastrophic failures, but could have a very small internal failure you cant see), but for 5 bucks ill swap it out and see what happens.

On the 95 trucks it is right above your accelerator pedal under the dash. On every year after I believe it is under the rug below the drivers side seat. 95 was a weird transition year for these trucks and has some odd differences from the 96+ models.
 

Blue Turd

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SOLVED!


I have finally tracked down the issue with my airbag system and have tracked down the parts to repair. The airbag light now blinks as it should, then goes away. I will write up everything I have learned below so hopefully it will help someone in the future, as there isn't that much information available on this subject. This information is applicable to all driver airbag only vehicles which is any GMT-400 based trucks/suv (and even some S10) from 1995 and 1996. 97+ Might share some similarities, but very likely a bit different due to having dual front airbags.


Background:

I has been almost a month since my last post, but in the mean time I have been poking around testing every airbag component on the truck trying to find the problem. The problem ended up being the airbag arming sensor, which is located in the driver side frame rail. It is right next to where the front section of the frame becomes boxed in. This unit is what powers the airbag computer and the airbag itself with airbag level voltage (36 volts). This is why my airbag computer would not flash the light, and my friends at the shop were not actually able to pull the codes. Even with an airbag fault, the system should flash the airbag light then stay lit. Mine never flashed, and was always solid.


Diagnosis:

First thing first was to check all the sensors for proper resistance and to check all wires for ground, power, and connections to all sensors. Posted below is the wiring schematic. Testing sensors is easy by checking your sensors resistance values to what is posted in the schematic. If it is an open, short, or wildly different value, the sensor is most likely the fault. For example I had previously posted my front impact sensors as being about 8.4k OHMs which is within spec, and therefore still on the truck working. The arming sensor on the other hand, had a couple pins open, when there should have been a resistance value. This ended up being the component throwing the airbag light. All of the connections listed in the schematic are for the most part properly labeled to the same number listed. If it is not, seeing the wire color behind the plug is easy to double check you are testing the right thing.


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From checking all of the wiring connections and sensors, I had come to the conclusion the the arming sensor was at fault. It didn't test properly and left a constant solid airbag light. The part number for the arming sensor is 16162465. There is 0 information on this part. Not even a single good image. Only links that come up is a couple GM parts websites saying its discontinued (with a ****** diagram that is of no help). For future reference here is the unit removed from the truck. It is held on with 2 13mm bolts.


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Heres a few of the inside as I promised I would take apart what ever sensor was broke. Nothing too exciting, but it did make a mess!


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Now tracking down this part was a complete PITA. Being discontinued no dealer will help you out, nor could I find any for sale online (even in used condition). Because my nearest pick and pull is quite a distance away, I looked online for about a month for the part, with no good leads. After that I decided getting the part myself was the only option, I planned a trip to my nearest pick and pull lot.


Luckily these trucks are plentiful, so finding a decent example was not too difficult. For the single airbag vehicles like my 95, I could only pick from the 95 and 96 model year GMT-400 platform vehicles. 94 and below did not have airbags, and 97+ was a dual airbag system (might still share some components, but I was playing it safe). I was able to pull a sensor from a 96 Tahoe that looks to have not been in any collision. One that has had its airbag deployed I believe would still be fine (hey it worked didn't it?). Amazingly this Tahoe didn't have any rust underneath, so this sensor was in much better shape than my own. Now if I was really on top of it, I could have brought my multimeter and tested it before leaving, but I didn't think about this till I was there. Just looking at the sensor and seeing it was in good shape was good enough for me to "risk". Satisfied with this sensor, I took the front crash sensors from the same vehicle as they were also in good shape. They will come in handy later. The junkyard cost me 16 dollars for all three sensors.


Upon arriving home I plugged back in all the components I had unplugged (so the airbag wouldn't randomly blow in my face), and plugged in the new arming sensor. Crossing my fingers I started the truck, and to my amazement the airbag light started to blink! Crossing my fingers even harder I watched as the light then finished its last diagnosis blink and went away. Yay success! The truck no longer has an airbag light, and will not be an issue when I have to go through Virginia's annual state inspection.


With the system back to working order, I plan on removing all the sensors from the truck again for clean up. I plan on adding some additional silicone in the small cracks in the rubber beneath to keep water out, then repainting to keep them from rusting any further. Even if you don't have any airbag problems, it would be a good idea to inspect all the sensors and seal/paint to keep any issues from happening in the future. These are all solid state devices, so if you keep them in good shape they should never give you any issues.


Hopefully this information will help someone out if they come across a similar issue. If you have any questions feel free to ask, I will try my best to answer them.

Here is the list of parts and OEM parts numbers for future searches:
Arming sensor - 16162465
Front left crash sensor - 16228285
Front right crash sensor - 16218905
Airbag computer - 16176557
Clockspring - 26087273
 
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CrustyJunker

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Thanks a ton for following up on this! Can't put a price on this kind of information. You went a lot more in depth than I ever did... And I discovered the same thing when I had my problems. No dealer help, and the web was just full of questions with no answer. Even the guy at my local junkyard asked "what even is that?" when I set one on the counter at checkout. It's a trick jewelry box with a cord on it.
 

Blue Turd

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Yep no one knows anything about these parts. Every yard I called that would pull it and ship to me had no idea what I was talking about. The few that sorta knew about crash sensors only knew about the front two, and wouldn't even sell to me for "liability reasons". I will edit my last post to include all part numbers for all sensors and the airbag computer, hopefully to lead anybody searching to something relevant with pictures and schematics to start from. After reading this entire thread again from start to finish it was like a log of what I was thinking at the time, as a lot of it was proven and disproven as I moved along.

Glad to help with the information. Its the least I can do to repay the members here for all the information I have found useful on this forum.
 

Blue Turd

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Here are my "refurbished" sensors. Got as much rust off as I could, then painted with rust reformer. Finally painted with a high quality enamel paint. I was going to originally do undercoating or bed liner, but decided against that because it requires bare metal to apply, and I really wanted the rust reformer paint.

The bottoms were filled up with all purpose 100% silicone.

This should help these sensors last many more years by keeping moisture and corrosion out.
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Blue Turd

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UPDATE:

Airbag light randomly been coming on and off again. Solid red light with no flashes, so that means the SRS computer isn’t doing anything. If the light flashes before turning solid read that means the system is working and has sensed a fault (you can read the fault with the proper scan tool).

I took the entire dash out to trace down the entire SRS harness, because there must be a broken power or ground wire somewhere.

I found the main SRS ground wire, which could have easily been fixed from underneath without dash removal....
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It’s located right next to the parking brake release. It looked good (and the other dash ground that shares the SRS ground was fine too). Simply removing and cleaning up this connection made the SRS system work again and predictably.

This was probably the issue the entire time, but finally solved all of my airbag issues. Hopefully someone can find this thread helpful if they come across a similar issue.

This thread has sort of turned into the go-to GMT 400 airbag information page lol.
 

Blue Turd

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UPDATE AGAIN:

So I reassembled my dash (way better than the last time I took it apart, no more rattles). Of course the solid air bag light was on again and I was livid!

So I traced the plugs again, and discovered that the two main ground cables for the SRS computer have a 20ohm resistance back to the negative battery cable. The one I mentioned in the last post under the dash is still good (it’s the system back up ground). Jumping the two main SRS computer grounds to a known good ground makes the system operate as it should!

So I have found the source (last time I promise!) of the issue finally. Now I just need to find where that bad ground point is.

Anybody know where the main harness coming out of the firewall from the dash grounds too? I don’t see anything obvious.

Otherwise I might just run my own ground wires to a good know ground.

Electronics 101: a bad ground is a helluva drug...
 

east302

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Not sure which ground you're needing, but it looks like the choices are G200, 201 and 202. Diagrams are for a 1998.

Hope it helps. I have a steady SRS light on only when it's cold outside. It started after replacing the turn signal switch and removing the airbag to do so.

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200 and 201 are on the firewall...

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They started with G202 and built the truck around it...

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Blue Turd

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Wow thanks for the diagrams! Looks like G200 and G201 are the only interior airbag grounds. Those are the two wires I took a photo of when I had the dash out. That must mean that I have a short somewhere on the SRS harness ground wire to ground (shows resistance to ground even when unbolted). I just decided to run my own ground wires from where it plugs into the SRS computer to a new ground I made a couple inches from G200/201 on the same bar. My issue is now solved and my airbag light blinks then disappears like it should.

Even if I discovered this with the dash out (course it all tested good when it was out!) it would have been a huge pain to dismantle my entire harness. If I ever have the dash off again I’ll maybe give it a look.

I’m happy with my repair though, and knowing that I did ground it to where it should have been grounded should give no problems. Worst case the solid airbag light comes back on, then at that point I will probably dismantle the dash again to see where my harness was cut into. The system should otherwise work as intended, and in my case, pass state safety inspection again.

I’d like to once again that you all for your help. This forum is always the best resource for GMT400 anything.

P.S: future air bag light search result readers, it’s probably best to diagnose your issues in the reverse order that I posted, starting with checking grounds and connections, then trying to replace parts. Solid red with no blinks is always going to be a SRS computer issue (wiring or actually dead module). Blinking then solid red airbag light is usually a sensor fault, but you can read the codes to know before buying something you didn’t need!
 
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