Through all of this, we need to define SBC failure. A generic " the SBC system failed" is like saying "the engine failed" , there is a wide range of possible failure.

For it reaching the service limit and shutting off, I'd expect the MB SW _NOT_ to shut it down in flight and rather have it wait for the next key cycle. And remember, it gives plenty of warning, as in about 1/2 way to the limit.

Now, for the sudden failures , any small part of any system can fail at any time without warning. I'd hardly fault SBC for that.

Looking at the hydraulic diagram, the backup MC only operates the front brakes in the event of a total SBC electrical system failure. So yes, there will be a hard pedal and brakes only on the front.

If the pump or it's control circuity fails, there will still be a few powered stops left until the accumulator is empty.

The accumulator is emptied via a solenoid valve. If the unit shuts off, you have no access to that fluid. If it shuts off, you're left with the emergency MC and poor braking power.

Sometimes MB does things well, and sometimes poorly. You'd think the SBC would wait to shut off, but you'd think the biodegradable wiring harnesses would wait to disintegrate until they're junked. We know the latter is not the case.

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Most of my friends with malfunctioning ABS, got rid of those vehicles. They were replaced with newer vehicles with ABS that hasn't malfunctioned (yet).
My friend with the '95 Camry has stopped driving it, not because of the ABS (which he got used to as it only kicked on at very low speeds) but because the waterpump failed. It's a $$$$ job on a Camry V6, so he's looking for a replacement, and driving a relative's 2002 Nissan Sentra.

Happy Motoring, Mark

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DrDKW

This is more like they wont do it. Either tech is inexperienced, or dealer does not want to do anything that adds even a remote possibility of liability -- "oh, you artificially increased the number of actuations! I'm going to sue you!" thing.

During normal operation, yes the SBC system gives you a warning almost halfway before the threshold. You'd have to intentionally ignore the warnings before SBC quits. As you get closer to the threshold, the warnings become more and more insistent....second white message will turn on the brake light, the ABS light and the traction light, plus a check engine light. And it might induce limp home mode or not -- I did not replace the SBC in a car that has gotten to that point.

That's right, my personal knowledge that I gleaned from MB informational documents and experience with replacing SBC doesn't mean much. I'm just a kid, after all.

Yes, I have replaced the SBC prior to failure. Would you drive a car that tells you the brakes will fail? I imagine that a lot of owners will cheap out on various parts in the car, but stopping the car should take immediate priority over all else, doesn't it? The owners of those cars were being proactive, as they are family people and have kids.

Yes, I can actually provide proof for my conjecture.

Welcome to the W211 E- Class!
Welcome to the W211 E- Class!

All these were in the MB educational informational documents. Pay attention to the last paragraphs at the bottom of the page.

I am sorry that your SBC failed without any prior warning, but like any other cars, glitches in the system can cause immediate failure. Perhaps excessive current burned out the SBC module, leading to failure. Perhaps the passenger side SAM module failed, which led to wildly fluctuating voltages and signals which led to module failure. Whatever it is, there are a lot of components in the car that are linked together, and it's possible that one component in the car failed and it led to a cascade failure of others.

Again, I only can speculate in your case. Did you ever find out why it failed?

This makes it possible to achieve the legally required minimum deceleration of 0.3 g with a pedal force of 500 N.

Possible- not probable. It also means it may NOT be possible unless you apply the full 500n of force; you may get NO braking at all. More than a few owners online have stated there was no warning whatsoever when their SBC brakes failed. Why on earth would you try to deny that? What do you have to gain?

OK, once more, with feeling.

I stated that if the pump fails, at minimum, assisted partial braking will still be availible for a limited number of applications. This is covered in the " Fall back level " statement " A " ( my lettering ) quoted at bottom from Welcome to the W211 E- Class! and by careful reading of the hydraulic diagram Welcome to the W211 E- Class!

Looking the hyd diagram, brake actuation solenoids y6 / 8 / 10 / 12 are normally closed. I'd expect this condition to continue the pump fails. This is also supported by the " Wake up function " quoted below.

Solenoids Y7 / 9 / 11 / 13 must be closed by applying electrical power to allow powered brake pressure to rise. In the event of pump failure, there is no need to dump system pressure.

As for the shutdown timing and bio wiring, you are mixing software programming and chemistry. It would be a real stretch to think the programming was purposely designed to shut the system down _in flight_ just because it hit the max brake applications. It is trivial to program in:
IF BRAKE_APP = 600000 and WAKE_FUNCTION = 1 then RED_ERROR_SYS_OFF = 1

MB didn't design the SBC on it's own, Bosch was also involved.

"" Wake-up function
The aim is to wake up the SBC before the brake pedal is first operated. This enables the reservoir to be replenished, if necessary, by operating the reservoir charging pump. In addition, . . . ""

"" Fallback level
Specific deactivation levels are incorporated in the SBC depending on the severity of a fault defined in the system. The individual fallback levels are listed in the form of a table:

• A — servo assistance by means of muscular power brake at front wheels and brake pressure buildup by SBC at rear wheels (active braking force assistance).
• 
  
• B No braking force assistance (only hydraulic backup at front wheels). ""
  

I don't know who you are responding to but, I'll pick it up.

You make it sound like a binary choice.

If < 500 N force then braking = 0G
If >= 500 N force then braking = 0.3G

Based on the hydraulic diagram, that isn't true. Backup braking force is proportional to foot force as this system does not have a pressure reducing or sequencing valve.

The "making it possible" statement pertains to the backup unit ( Master cylinder ) in the sense that " The operating unit ( 1 ) exists as a backup in the event of a brake by wire system failure that inhibits the computers ability to control the solenoids. "

The MB dealer in Appleton WI told me they COULD not determine SBC actuation count. I discussed my concern about the shutdown of the system and the service advisor had no answer.

I will be purchasing a DAS clone soon and have read on various forums that in developer mode the SBC actuations can be determined with it.

John

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Unit fails before warnings of lower remaining expected life cycles pop up. No indicator other than red light perhaps and no brakes. Sounds like some units do not make the count even till the white light stage.

Here is where it gets really stupid. Unit is still functional but expected life cycles are reached unit gets shut off. Normally I would expect the white warming presented though in that scenario.

You want to play games like this on cars then aircraft redundancy type systems must be employed. Maybe their engineers at that time were doing substance abuse. Or liked Russian roulette.

My guess is either they rethought what they had done. Or more likely some of the units failed very early in service causing accidents. Even electrical faults can probably shut the brakes down. So they just eliminated it from future production.

Lots of great information in this thread… Thanks to all who have replied. While I need to continue my research, I guess my overall impression is that I'm pretty content having a car with SBC. I don't mind the eventual expense and from a safety perspective I'm confident I'll be fine... Though of course not certain. I guess it will always be in the back of my mind.

I don't understand. You think that unless you press 500+ n of force, you won't get the 0.3 g braking force?

Like 97 SL320 said, it's not binary. You do get braking force...the more you press, the better the braking.

And I guess you didn't read my post fully, but I'll quote myself again:

See? Nowhere in my post I mentioned that you will have "full" braking force. I don't know where you got that.

As I understand it, you need 500 n of force to get the minimum required 0.3 g braking force. Below 500 n would provide less than the minimum g and above 500 n would get more.
0.3 g braking is still very weak.

But what really bothers me is that it sounds like, while the SBC system may still be working adequately, it's programmed to shut itself down after so many cycles.
I can understand an electrical or mechanical failure causing the loss of the system. But to program a working system to deliberately shut itself down, leaving one with almost no braking, is ridiculous! Even assuming there WERE reminder notices, shutting off a working safety system because the owner ignored the service reminder makes no sense. This is NOT the same as ignoring oil changes. If there WAS some compelling reason to design a working SBC to shut itself down, they should have at least designed it to disable the vehicle or go into limp-mode before shut-down. Like the Ad-Blue systems in the diesel cars.
Oh well, I guess protecting the environment trumps protecting human life these days!

Happy Motoring, Mark

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DrDKW

Concerning the above, the SBC shutdown is a valid strategy, it issues warnings long before lockout then eventually shuts down. Using the data provided by Deplore:

"" The white message shows up around 350,000 to 450,000. The second white message shows up at 500,000 and up all the way to 600,000 -- and then SBC deactivates itself with a red message. ""

So, around 58 to 75 % expected SBC life, a white warning is issued, another white issued again at about 83% of life. When the counter hits 100% of life, the system issues a red warning and locks out. I would not expect the system to stop functioning in flight due to a life limit counter. Do you have documentation that once the counter hits a certain point the system locks out in flight?

You need to separate a random component failure from a "The SBC system needs changed" counter, they are completely different shutdown modes.


For a planned shutdown, there is plenty of warning. If someone chooses to drive the car after the SBC has shut down, they are at fault not the car maker as this is no different from driving a car that has brake pads completely worn off.

Some here have claimed they saw NO advance warning, or that sometimes there is, sometimes there isn't. So please clarify.

Does the advance warning remain on until planned shut down, or does it go out after a very short time?
If it goes out and the driver somehow ignored or missed the warning, does the planned SBC shut down occur while driving, or does the system 'wait' until it's 'safe' to shut down?
Does the braking go into 0.3 g mode merely due to a planned shut down or only if accompanied by component failure?
Is there is some compelling reason to have a planned shut down of a working SBC without component failure?
If so, why not either have it disable the vehicle, put it in limp-mode, or at least have a constant red warning light and annoying beeper operate well in advance, up until SBC shut down, like those I've seen in older Mercedes when their ABS/stability-control systems malfunction?
Or is this a new 'You WILL maintain your vehicle on our schedule, or our system is programmed to KILL you' strategy?
Enquiring minds want to know!

A final note - I have driven vehicles with brake pads completely worn off, and they typically still manage to generate way more than 0.3 g braking power, accompanied by so much noise, for so long before total brake failure, that only the most obstinate driver would ignore the problem.

Happy Motoring, Mark

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DrDKW

During a sudden SBC failure if you get better braking the more you push then the clearly the amount of braking is dependent on pushing harder with the maximum being .3g's (translation- very little). If the driver is incapable of pushing hard you may get little or zero braking power. The quote was "it is possible"; means it is also NOT possible; meaning you may get zero braking- or braking slightly better than coasting to a stop. That's not much help at 75 MPH on I-95 during rush hour if you are wearing heels and you are a 65 year old 110 pound lady. In reality if your SBC fails you may get braking marginally better than coasting to a stop; and that is the experience many drivers who have had SBC failures have related. Also in reality you may get decreased braking that ends up being a minor inconvenience when your SBC fails.