SRS/Airbag diagnostics and diagnostic tools
Good morning every one. This is my first post on Diagnostic Network and I'm hoping to learn from you all on a topic that I've thinking about lately. The topic I'm hoping to get information or advise on is SRS/Airbag diagnostics with the use of a "load substitute" tool or the use of varying resistances. I'm still a young tech and have been taught that when diagnosing Airbag faults you should use a ohm meter. While i still think it is a tool to use in airbag faults over the years i have developed an attitude of that is to much work and is not good enough for me. I have heard of people using varying resistances to put in place of an air bag to verify if its a wiring or module issue or airbag/ component itself with the help of a scan tool. I like this idea and am hesitant on using it due to not wanting to make things deploy manly because I do not fully know "X" component should have "X" resistance. So i'm asking for knowledge from you all out there that use a load substitute what exactly do you use, is there a tool i can buy or something you can build? Also what safety needs to be taken into account when using a substitute?
I have a 2009 G6 with airbag light on and airbag system fault message. Fault code B0013 Driver steering airbag deploymnet loop stage 2 resistance above threshold. When one looks uo GM SI for this fault, circuit/system testing indicates the use of load tool adapters.
You are thinking correctly about the use of an ohm meter with an airbag still plugged into the circuit. DO NOT do it.
An ohm meter uses a battery, which could send power down the circuit and deploy the airbag. Most of the OEM's do have special adapters that have the correct resistance to plug into the specific airbag connector to "take the place" of the actual airbag for diagnostics.
I personally have not used any type of "generic" airbag resistors for testing. I came out of a Ford dealer and they had the specific resistors with the specific connectors for each year, make and model as they changed. These specific special tools will also dis-engage any "shorting bars" in the connector once they are plugged in. It is always best to use the specific airbag resistor with the correct connector, for the year, make and model you are working on.
With that begin said, if you knew the exact resistance of the airbag, and installed that specific resistor in place of the airbag for a "quick ohm check" on the circuit, that could work. Be sure to isolate your circuits as to not effect other airbags with in the vehicle.
If you have a scan tool that will allow you to see the resistance of a specific circuit, let's say, the driver airbag and the spec on a normal circuit is 2-3.68 ohms. If you can monitor that pid and it is 8 ohms, you know you have a problem there.
If you unplug the airbag, remove a "shorting bar" if the connector has one-your resistance will change, should go "open". If the "shorting bar" is left installed, your resistance should go to "short" or very low. If you do either and the resistance does not change on the pid, you are looking at a short or possible module issue.
I have looked into this in the past, and have found companies selling fixed resistance value tools for generic applications, the oe tools, which in Ford's case can get quite costly, or the variable resistance type. Currently I am thinking about getting the Kent Moore J-36884-A, because it can be adapted to be a universal one, and it goes from 1-14 ohms. If you search ebay for airbag tester, you will find a lot of options.
Thomas, If you can find a resistor with 2-3 Ohms of resistance that will work just fine, and if I remember correctly several of the park lamp and break lamp bulbs have the correct resistance and you can run some wires from it to simulate. Another way is to short the wires together as see if the code changes to a below threshold. As stated if using the resistor ensure on there is not a shorting bar where you insert it. If I’m not mistaken the driver bag has a shorting bar internal so it is out of the equation when you remove the bag, but the connector at the bottom of the clock spring might very well have one. Let us know if your unfamiliar with the shorting bar and or its purpose.
Hey Don thanks for the reply. So believe I know what the shorting bars are. When I disconnected the connector from the steering wheel coil I saw that the 4 female pins had what I’d describe as metal tabs hat had tension to them. Please correct me if I’m mistaken. i wanna make sure I understand if I unplug the air bag and the shorting bar is say in the clock spring then I CAN NOT use the resistance in the circuit? also what is the meaning of 1st stage and 2nd stage? Thanks
Correct the metal tabs with tension are the shorting bars. You can use the resistance in any situation but You must raise the tension on the bars. Toothpicks work well to place Between the terminal and the bar. Also look for code change If the shorting bar is on the connector when it is unpluggeg.
Stages are for the force need in the deployment. The vehicle monitors several factors some obvious like speed and Change in volicity to determin wether to deploy one or both stages, but most will also factor In if the drivers seat is positioned closer or fwd to the steering wheel or back as well as seat belt status.
Hope that helps.
Hi Thomas. Please discontinue Ohming SIR/Airbag system circuits unless directed to do so, for your own safety, as has been mentioned elsewhere. When a deployment loop excessive resistance DTC sets, the scan tool will display the resistance of the related loop.
As also mentioned, we utilize tool with the appropriate adapters of which there are many. Yes, you can use a resistor to substitute a componet iif you are aware of the desired loop resistance. Let’s move on to say that you have eliminated a driver’s or passenger front air bag by subsitution using a resistor, since the loop resistance didn’t change.
Now, you may be directed to test the circuit manually, between the SDM (air bag module) and the airbag component connector (main harness side). Make sure that the system is de-powered. and wait until disconnecting the components. You might be required to test the deployment loop from the SDM to the steering wheel module connector.
To Ohm the harness between these two points with it disconnected at both ends, you can now use an Ohmmeter to check each single conductor in the affected circuit. However, you must first lift the shorting bar contact at the SDM harness connector. The easiest way to do that is to remove the TPA (Terminal Positive Assurance) insert from the connector at the SDM end of the harness and gently lift the shorting bar to allow measument of only the one conductor, otherwise both conductors to the air bag will be connected, skewing the results. Each stage will have a pair or conductors with its own connector on GM vehicles.
Thanks for the reply Martin. Unfortunately the Tech 2 did not offer but 4 pids in the SIR module data. Battery voltage, airbag request lamp on or off and 2 others that did not lend a hand in resistances. Thanks for your time and information.
This kit from AESWave has a special adapter that can be used to check airbag circuits. Essentially you can just use resistors that you could purchase from Radio Shack (if they were still open) but this kit has many other uses as well so if you were considering purchasing a tool dedicated to airbags I think you will find this kit has plenty of other uses and you'll end up using it more and more as you get further into diagnostics. aeswave.com/uTest-Advanced… There are a few resistors in this kit that can be used with the tool but I don't believe I have switched them since I've owned it and used it across many carlines. I believe I've had the 3 ohm resistor in the tool and it has worked for just about everything. Essentially the module is looking for a specific resistance through the airbag or seatbelt pretensioners or really anything with an explosive (I know there is a better less threatening term but it escapes me at the moment) device meant to deploy in an accident. Side note: Aside from just airbags and seatbelt pretensioners, these devices are also being used to deploy hood hinges and disconnect battery terminals and probably plenty of other things I have yet to run into. As for being hesitant I felt the same way around airbags at first. A few things to keep in mind: 1. It's important to keep your power probe off of these circuits. If you apply a power to the circuit you can deploy the airbag. The same though applies to an ohmmeter. Because an ohmmeter must apply a power to the circuit in order to check the resistance there is a potential to deploy the airbag. I have at times used an ohmmeter to check airbag circuits but ONLY with the circuit disconnected and the deployable removed from the vehicle. In most instances resistors eliminate the need to use your meter and make the diagnostic quicker. That being said I collect airbags to deploy at the school I teach at when I am teaching that class. I have tried many different brands of voltmeters and many different types of airbags and have yet to get them to deploy one as they don't put out enough power. I feel a little safer knowing that but I'm still not willing to try it in a vehicle. 2. Airbag modules have sensors in them that can detect if the vehicle has rolled over. I recently visited a shop where a pretty competent tech had to remove the carpet in a van for an unrelated service. Halfway through the oil truck pulled up and he needed to move the van to make room for the truck. He had forgotten that he had unbolted the airbag module and left it connected flipped upside down, out of the way. As soon as he turned the key on to start it all of the curtain airbags deployed. As for the testing, the airbag module can tell the condition of the airbag and circuit by looking at the resistance through the circuit. If it expects to see 3 ohms and sees 0 it will set a shorted code and if it sees infinite resistance an (open circuit) it will set open codes. Many scan tools will also show the resistance read by the module as a data list. This can be helpful but if it is not available the code clearing method will work fine as those codes set immediately. In the instance of a steering wheel airbag the two wires from the module create a loop to and from the airbag. The airbag should be the only point of resistance and the module is acting as it's own ohmmeter. If it sees the three ohms it expects to see on that loop it knows the airbag and circuit is ok. By using the resistor as a substitute you can easily diagnose a bad clockspring. If you remove the airbag and install the resistor so that the module is now checking the circuit through the clockspring and the code goes away you have verified that the clockspring is ok. If the code does not go away you can try the resistor on the other side of the clockspring. If the code clears you have verified that the loop is intact up until it goes through the clockspring. If the airbag has 2 deployment loops those are two separate loops.
Mike thanks for your time and knowledge it is greatly appreciated. I have my own story with an airbag module actually, however i was luck enough not to have deployed anything. I had a Mercedes Benz 204, C class. the passenger seat had been moved to the maximum position forward it would go, the cable had broke off under the frame and motor was striped so i could not get the the two front bolts holding the track/ seat to floor. My only solution I could come up with to move the seat back enough to unbolt the front bolts was to take my air hammer and hit the tracks back n forth, trying to move the track back little by little. It didn't matter that the track was being damaged because i had sold a new track, motor and cable, the problem was i did not stop to think about where the air bag module was and how close the air hammer was to it. The air bad module sits forward the center console and my air hammer was up against the console. So i finally got the seat removed and repaired and back in the car. I then started the vehicle up to work the seat back n forth and there was the airbag, srs and service airbag message displayed on the IC. I hooked up Xentry and ran a quick test and found numerous faults for air bag module and sensors. The hard vibration of my air hammer, I'm guessing, shook the module so hard that it damaged it. Bought, SCN coded a new airbag module it all was good. A lesson i will never forget.
Glad nothing blew. I've heard stories of the impact sensors getting hit and deploying bags as well but I think that's pretty hard to do and/or might be a myth. You can't learn and grow as a technician without running into things like that. I used to beat myself up over those things. At the end of the day half of the services we do require a battery disconnect which now involves 20 minutes of relearn procedures. If we did that every time it was called for we would be called slow unproductive techs but even worse we would probably not be able to feed our families. Learn from it but don't let it scare you into thinking you need to unplug every airbag module every time you break out your air hammer. Guys will tell you you must unplug every computer from the vehicle to weld on it. Good luck doing that on an 8 series. And even better luck getting paid for the time it would take to unplug every module on that car! So sometimes things like that happen but it's just part of what we do.
So I was wrong I've been using a 2 ohm resistor. This is what I had mentioned from AESWave kit. Inside of the cap there is a little resistor. These are interchangeable and a few come in the kit.
Here is a sample diag on a Chrysler 200 using that kit. Vehicle had a code for the deployment loop in the seat.
Here is the wiring diagram identifying that circuit.
All I had to do was install that tool in the connector at pins 8 and 9. Here is another view. I didn't bother testing at the component itself because it is sold as an entire seat.
As you can see here the code cleared and the diagnostics was complete.
As you can see these are very simple and quick diags!
Mike really like the photos thank you! I'm more of a "show me and let me practice" type. I'm sold on that aeswave kit. I've been eyeing that kit, the relay jumper/measurement tool and the DLC BOB.
I use a variable resitor that I got in an automotive electrical test lead kit, its very accurate(as measured by my fluke) I cant remember a time when more than 2.3-2.5 ohms was needed.
How do you dial in the resistance?
Didnt realize the picture was blurry. The black portion around the gauge turns. Right now it is set at 2 ohms.
I have that same kit and it makes testing stupid easy. For instance, say you have a code for driver side squib open. Remove airbag from steering wheel and insert the resistor. Code gone? Airbag is bad.
Or, lets say the Code is still present? Step 2 would be to unplug the harness on the opposite side of the clockspring and insert resistor. Code now gone? Bad Clockspring.
Pretty simple, with one caveat. Sometimes "open" is really just higher than normal resistance. If the harness proves out good I would put some stabilant 22 on the connector and plug the squib back in and see if the code goes away before condemning a component.