Air Bag Diagnostics

[way]

Hi,

I bought a 96 Metro LSI (3 cyl, 5 sp) that was originally bought as a rebuildable salvage car that was going to be converted to a solar car. The project fell through and it sat in the guy's garage since 96. He lost the title and yada yada yada, a little over a year later and now 6 months after that, I've got the car 99% put back together. It now has a total of 995 original miles on it. Trouble is the guy who put it together does not do air bags as he's strictly a body man.

A friend of mine has a garage and he couldn't find the plug in for his scanner.
I'm trying to avoid taking this to a dealer if at all possible only because of how expensive the one nearest me is. I've got about $2500 total into the car so far and I'm trying to not spend too much more (though if I have to, I will).

Does anyone know where this plug in is located? I think it's on the driver's side but my friend doesn't seem to think so. What exactly does it look like?

Also is there a good site for the trouble codes as well as info on resetting the system? The air bag light stays on constantly and we've tried disconnecting the battery overnight but no go. Is there some magic procedure?


Thanks

[hot_sd]

I've not worked on the airbag system myself but having looked at the factory manual in the past about how the airbags work this is what I understand - the airbag error codes are also sent to the OBD2 connector which is located under the driver's seat. However, the normal connector on which the engine data comes out is pin 7. In the Metro pin 9 is is used to send out airbag data. I am assuming that if you take a regular OBD2 code reader and make an adaptor which takes out data from pin 9 on the DLC and sends in to pin 7 of the code reader should be able to read and reset the codes. The airbag codes usually tend to be not universal across cars so you will need the factory manual which explains all the codes.

Depending on what you need to do you may need additional tools to work with the airbags and be careful you do not accidentally deploy them. Get the factory manual if you plan to work on it as it tells you how to disable it etc. Check out ebay as I do see some of these tools selling on there for reasonable rates.

[way]

Hi SD,

I took a look-see under the driver's seat but there appears to be nothing there besides the seat belt wire.

I managed to get my hands on a service manual which shows an airbag diagnostic connector by the steering column which I found right off. It has a black cover on it but it looks nothing like what my friend said he was looking for which I presume is the OBD2. It sounds at the least that there's an adapter involved here.

My friend has the software that tells what the procedure is for resetting the codes for Metros but he apparently couldn't find the OBD2 connector.

Are those tools on ebay listed under OBD scanners?


Thanks for your help

[hot_sd]

Yes, sorry I just had a moment last night to browse the forum and typed rather quickly - yes, correct what I meant was under the dash on the driver side - that's the OBD2 connector - I have read codes out of that (mine's a 2000). About the adapter - to clarify - OBD2 serial data out of the ECM comes out of pin 7 on the connector. However, according to the factory manual the airbag computer (which is a separate unit and lives near the gear shift lever) sends its own data on pin 9 so I presume that making a adaptor which takes the signal out from pin 9 and sends it to pin 7 on a code reader should allow the code reader to read the airbag codes. The code readers/scan tools will be expecting the data to be present on pin 7.

[way]

Ah ha. LOL The connector I found was on the yellow air bag circuit. I'm presuming it's easier to use the OBD2 connector? I think that's what he was having trouble finding. I guess the idea is to run a jumper from the Metro pin 9 to the scanner's pin 7? I kind of used to do that on our older gm cars to get a code from the check engine light. Doesn't seem like a complicated system except for finding the connector.
Is it a normal looking connector or is there some difference in the Geo that makes it hard to identify? There's only so many places to hide it in a hatchback.

Here's what I found so far:

[way]

Is pin 9 the one on the lower left?

[hot_sd]

That's correct. Pin 1 starts at the top left and then 9 starts at the bottom left and goes to bottom right which is pin 16. As you can see only the pins with the silver connectors are actually used. For those interested in OBD2 - 4,5 = gnd, 7 = serial data (ECM), 9 = serial data (airbag), 16 = System positive voltage.

As for making the adaptor - I guess you can find a way to jumper the connection. I cannot remember offhand what the data rate is but it is probably low enough not to cause problems if you did this. The nicer way to do this would be to get 2 OBD2 connectors and make up a cable with the signal crossover. Maybe GM makes such a cable assuming they do the same for all their vehicles. If the data rate is high you would have to make a proper cable with connectors - othewise you can get problems with things like parasitic capacitance as well as reflections due to mis-termination (transmission line effects) etc - all which will distort the data and cause the reader to not function properly.

I think that connector you found is used for "flash diagnostics' - you can get the airbag light to flash a given no of times to figure out the fault code by jumpering two of the terminals together. You cannot clear the codes using this connector.

[way]

For those interested in OBD2 - 4,5 = gnd, 7 = serial data (ECM), 9 = serial data (airbag), 16 = System positive voltage.


I'm extremely interested LOL

I'll give the car a going over this weekend/early next week and let you know how it goes.

I really appreciate your help on this

[hot_sd]

Well in that case - I double checked the info on the web The metro uses a variant of OBD2 called ISO 9141. This uses standard asynchronous serial data at 10.4 kbits/sec. (asynchronous date normally uses a 16X clock at the receiver to sample the data in the middle). From what I can see the only thing that prevents this from being connected directly to the serial port of your PC and viewing it on hyperterminal is the non-standard baud rate - standard rates for computers and peripherals go like 2400, 4800, 9600 etc. However, you can find various simple designs on the web to turn your PC into an OBD2 reader although you will need to write some Windows software (using VC++ or similar Windows development environment) to write the interface and display the data. There is plenty of info on the web about the format of the protocol - fairly simple.

In short the data rate is fairly low so you can probably get away with a simple jumper.

[way]

Here's a scan tool I think will work:

http://www.obd2allinone.com/

They offer a connector for $5.95 which sounds safer than poking jumpers around:



Has anybody used this scan tool for the air bags? (96 Geo Metro Lsi 3 cyl, 5 sp)

If so, what protocol software did you use? You can pm me if you wish.

I've got extra air bags but I'd rather not use them if I don't have to.

[99Metro]

I thought that Checker, Autozone, etc will scan/reset codes for free. Then they get your business on repair parts. Might be worth a phone call or two to them to verify this.

[way]

I wanted to update this as I have finally fixed the problem.

Instead of doing anything fancy trying to get into the OBDII system I decided to just swap out the Air Bag SDM (Sensing and Diagnostic Module). I got one off Ebay for $25 and put it in. The damn connector was kind of tricky to figure out but I finally got it replaced. Started the motor, the light blinked 7 times and then .... IT WENT OUT.

And I swear, almost as soon as the light went off the transmission started making noise.

So anyway, this tells me that if the air bags go off, the SDM either has to be reset or replaced. It doesn't clear itself as I was told elsewhere.

There are also places online that will reset your air bag SDM for like $85 w/free shipping but I haven't tried any of them yet.



HTH

PS: 99Metro, thanks for the suggestion. I didn't see this response and I'm sorry I didn't answer you.
I don't know if they can read air bags though because it's a separate system from OBDII that they'd read. It's pin 9 in the connector which I'm not sure their scanners would pick up as that's different from the normal ISO9141 protocol. The air bag system is totally isolated from any other system in the car.

[way]

I'd also like to mention the clockspring mechanism. It's under the steering wheel air bag. It's basically just a doo dad that allows the wiring harness to rotate with the steering wheel and yet remain connected to the air bag. What happened in my car was that when the air bag exploded, it crushed the connecting wires together so that I had to separate the casings with a razor blade. The wires themselves were intact so I just wound them up with electrical tape and put the driver bag back in. Until I replaced the SDM I had this in the back of my mind that I'd have to replace the clockspring too which it turns out, I didn't need to.

I presume this type damage is common so just in case someone else sees the same damage, you might just do the same thing. As long as the wires are not broken, you should be able to just tape them up. Saves you the trouble/cost of replacing the clockspring.

HTH

[htpccaseLori]

I just found this forum and I must say that I'm glad I did. I hope to bring something to the community as I have already found some interesting topics. Hailing from the Dirty South (United States for those that don' know).