Airbag light came on. Errors pulled with an Autel scanner:
9B02, The squib for the driver airbag (stage 1) has excessively high resistance, MIL ON & stored
9B06, The squib for the driver airbag (stage 2) has excessively high resistance, MIL ON & stored
I'm quite surprised not to find anything on the internet about these codes. Anyone know where these "squibs" might live in a circuit? Or have a good description of the various sensors involved in the W212 Driver's airbag? USA, left hand drive, wagon.
No accidents, light simply came on while driving down the road. Have owned the car almost 2 years. I've cleared the codes and it comes right back on. I do live in Maine and it's cold here, but the car stays in a garage that's kept above freezing.
See attachments, check r12/13 & 14. In addition FYI MBUSA released attached recall that may affect your VIN you can check here: https://www.mbusa.com/en/recall and/or have dealer check Vehicle Master Inquiry (VMI).
For posterity. The squibs are the yellow and orange connectors with the purple/green, blue/yellow wires. I measure .001 ohms (basically, continuity) in and out of them which is a far cry from high resistance. My guess is somewhere else in the circuit is poorly connected, like the clock spring, and it's revealing itself as the error I'm reading. I'm going to go forward with the assumption the airbag and squibs are fine.
I have had the steering wheel off once, and I've recently had the driver's seat jump its track (kids left a water bottle under the seat), so I'll start checking for and cleaning and reconnecting things. Whee!
Thankfully, the scanner I have will let me clear codes, so I can poke around.
I think the airbag and squibs are good.
The scanner tells me the seat-belt clicked switch works and can give me real-time sensor resistances and system voltages. I can clear codes, but they are back instantly on startup.
Here are a few possibilities:
Clockspring
is not passing the data properly, though all other controls (horn, steering wheel buttons, etc. work. Replacement is $150
Do the circuits for the squibs go through it? They must.
Battery:
Voltage on main vehicle battery is hovering low at 12V, though it fires the starter powerfully and clearly the alternator is working (14.5V when running).
I have read some theories that lower voltage batteries cause all sorts of shenanigans.
Fuses / circuit
I've pulled and checked the fuses relevant to SRS. They're find
Anyone have any other ideas? Hate to just drop it off at an indy and have them throw parts at it that I can throw at it for less.
So here's a diagnostic process for others heading down the same path. Do you have "resistance to high" squib errors 9B02, 9B06?
Before anything else happens, it's probably your clockspring in the steering wheel. It’s the one part that moves constantly and is a fragile concept to begin with. I bet that's your problem.
Other possibilities:
The squibs in the airbag don’t have the proper resistance and are bad. Airbags themselves shouldn't ever really go bad. Again, no moving parts. Plus most of them were replaced in a recall in recent years anyway. Like a new lease on life!
The wiring is bad somewhere. The wires are going to be fine anyway. 99.9% of the time. Not a moving part, not a stressed part. However, checking continuity in the circuits described in the wiring diagram attached can be done by going to the three fuses in the fuse box in the engine compartment, which are linked with the driver's and passenger's main airbags: fuses 7, 15, 21. These blade style fuses actually have a test point at the top of them for meter probes. Turn the key to the on position and you can measure mV current drops across them, which means that the current is flowing in the circuit, which means that there's continuity between the fuse box and the Control Module. Meaning your wires are fine. There won't be a current flow through fuse 21, which is for the passenger airbag circuit, until you have a friend sitting in the seat for you.
Wires, however, have connectors at their ends. Connectors can go bad. The connectors to the control module are very well engineered and don't move or get stressed, so not likely the suspect. The connectors under the seats, however, do get stressed and can fall off, be broken off, get shorted by water, etc. Worth taking the seat bottoms off to check and clean them. Those of you with MBTex seat bottoms have already learned how to remove those.
The Control Module under the center console is bad.
Without appropriate reprogramming software, you really can't replace the Airbag Control Module under the console in that it appears to be keyed to the VIN of the vehicle itself. Well, that is, I bought one, and my scanner tool told me the car was complaining that the module's vin didn't match. $30 lesson. No big deal. If you do have that ability, they can be found used. To get to the Airbag Control Module for pulling the wires and checking continuity, etc. there are some excellent videos on YouTube. :
And so it is very likely your clockspring inside of the whole turn-signal/cruise/wiper stalks unit.
I diagnosed with my scanning tool (Autel 808), which shows the seat belt latches and the resistance in various circuits working real time. Resistance expected of airbags, where the squibs connect, is in the 2-3 ohm range. This means you should be able to replace the airbag in circuit with two 2-ohm resistors (one to each squib) and test again. I called them my virtual airbags.
You can perform this test this both after and before the clockspring: Test after the clockspring first because you don't have to pull the whole clockspring unit (turn signals, wipers, cruise stalks) or steering wheel unit off. Should it pass the test, your problem is the airbag or squibs in the airbags.
Disconnect battery at negative terminal, danger, your mileage may vary, I'm not responsible, swim at your own risk, no lifeguard on duty, etc.
Test after the clockspring by pulling the airbag (disconnect battery, pull airbag, reconnect battery) and its connectors to the clock spring. Figure out which leads from the airbag connector represent which squib (hint: they're the yellow connector, and very obvious by looking at the 2 wires each as they route to the squibs in the airbag itself. Put a 2 ohm resistor across the prongs on the steering wheel's side of the connector while watching your scan tool to show actual resistance. If your clockspring is bad, or intermittent, well, there you've probably found the problem.
To test before the clockspring in circuit, pull the clockspring unit (turn signal stocks and all) straight out and unhook the one connector to it. The pleathery hood around the whole unit will nicely disconnect all its tabs for you. It's hard to break it. Now you have access to the wires coming from the airbag control module. Figure out which pins represent the squibs and put the 2 ohm resistors across those. Hopefully your scanner will show you 2 ohm resistance across each circuit. You can do each circuit one at a time. If it reads in range (2 ohms), then your wiring is good. But it gets lost in the clockspring.
In my case, the clockspring was open circuit for squib prongs 2,3,4. Take your time shopping for used units, as there are variations in the stalk assemblies and steering wheel buttons and functions. For example, I have a wagon, which has rear-wiper controls on the turn signal stalk. Chances of finding one of those? Low. However, the unit can be taken apart to sub modules, and you can pull just the clockspring itself and use your original stalks and controller housings. So that's what I did. And now I have a spare piece of turn signal stalks of no value. But they are pretty.
You can buy just the clockspring component stand alone, but you probably won't find one used stand alone. All my internet searching led me to some "China will build you these for you! minimum order 1000 units" or, oddly enough, some ebay sellers in Australia. Huh. Not here in 'Murica.
When the clockspring has been replaced, you will still need a scanner tool to formally clear the codes. They get stored, not just lit up if there's something wrong.
It's nice to fix something by yourself which would otherwise probably put dollar signs in the eyes of a dealership. It's also neat to start the car and not have that warning come one.
Hi @Toadroller , thanks for the detailed write-up. I know this thread is a few years old, but my 2013 E350 wagon has also recently thrown an airbag light and I figured I'd update with any information I learn while diagnosing/repairing it. Funny that mine happens to also be a wagon, and even funnier that I'm also located in Maine.
My car has the 9B06 code for high-resistance at the driver's airbag squib (stage 2), but not the 9B02 (Stage 1) code. It seems like the clock spring is by far the most likely culprit, and I have one more data point to add: when I clear the code, it stays off until I start to turn the steering wheel. I'm not skilled or experienced with electrical diagnosis—in fact, just the opposite—but this seems like something I can learn. Unfortunately, I don't have a very sophisticated scan tool, I doubt mine will show resistance across circuits. I have a long road trip coming up in three weeks, so I'm hoping to fix this issue before that happens, and will update here once I've figured it out.
I resolved the issue back then by buying a used clock-spring unit (turn-signal stalks and all) off of Ebay. Because finding a unicorn unit from a wagon, which has the rear wiper controls on it, is very difficult, I bought a regular one from a sedan and took it apart to swap the bad clock-spring part. I like to take things apart and put them back together.
You could take the very good odds it's the clock-spring, buy a unit, swap it out with a used one without the rear wiper stalk control for your trip, and then do the take-apart process when you get back. Or do the trip with a likely disabled airbag. Your call.
My fix lasted me the last 3 years I had the car, which I had to give up on it in June when its rear subframe rusted through. Yep, Maine. MB actually honored replacing the subframe under a 20 year (!!) warranty, but enough other things wrong and rusty down there (would have had to redo most of the suspension links, the suspension airbags and struts, etc. put the bill around $5k. I gave in to temptation and picked up an 18 S560, which is nice. Though, knowing me, my next car will bring me back to an E-class wagon. It was so me. I miss it already.
As was suggested, I bought a used clock spring unit off of eBay (with the shifter stalk, etc.). I got SUPER lucky and happened across a wagon-specific unit with the rear wiper switch for only $140 shipped. It seemed that most of the sedan-specific units were closer to $250, so even though the wagon-specific units are hard to find, perhaps demand is also lower? I guess demand should be the same because production numbers would cancel out and failure rates are probably constant across wagons and sedans, but regardless my find seemed like a good price. I'm glad I didn't have to swap over the clock springs, as I was worried I might break something and cause myself further delays. I installed the replacement unit, cleared the airbag code, and everything is working perfectly.
Thanks again—@Toadroller—for your guidance with this. I'm a long-time BMW owner and while I love my S212, it's been harder to find DIY information for it online than it was for my BMWs. I still have a 2005 M3, which is a car that everybody beats on and tracks, so naturally there are tons and tons of repair info on the internet for that car. I'm hoping to replace it with an older Aston Martin V8 Vantage, for which there's very little DIY info available—that will be a big adjustment.
Enjoy the S560! Wagons are the best, in my humble opinion, but I'd swap my S212 for any newer S-Class in an instant!
Hey @E39 I'm thrilled for you! Finding the wagon unit on Ebay and at a bargain price? Win, win! M3s are sweet. The only BMW I've ever owned is my 06 K1200s inline 4 motorcycle. Smooth doesn't begin to describe the engine on that beast.
Regarding my wagon: when the subframe gave up this June, the local (65 miles away) MB dealer honored the warranty for it but, as I related above, other related repairs made it not worth the while or money, the service manager offered to buy it from me. I suggested $1000 and he shook my hand.
I was in that dealership last week and found him. He'd fixed the rear subframe and some other issues and was thrilled with it. He'd replaced his old Jetta with 350k miles on it with my wagon and has many more years of enjoyment left. Happy to know my old ride will live on.
Ask me about the 97 Audi A8 I bought in 01 for 19k at 78k miles and took to 265k before selling it to the kid at Autozone for $100. I do wring almost the full useful life out of my cars.
