m5zealot

HI Guys,

Well, I finally turned 90K miles last weekend. I recently got the entire ABC system replaced because I decided I'm keeping my SL55 forever! I also got the brake fluid replaced. A few days after, I noticed some hydraulic type noises when depressing the brake pedal at the rear of the car. I figured the tech may have not purged the system of air completely. I also noticed the SBC pump comes on for a few seconds after I unlock the doors. Fast forward to Monday - Got the failure warning and lucky for me, I was only a mile from home. The experience is even more scary than described in here. Without being in limp mode and engine downshifting to 1st or second gear....there is literally no brake pressure at all. If this had happened on the freeway I fear to think what would have happened if I had to stop suddenly. I have been doing the maintenance on the car myself but the ABC work I had done at my local independent. I had the car towed to my local dealership this time since we have a very good relationship with the service manager.

He is going to try to get MBZ to cover the replacement of the unit completely or partially since there was an extended 10 year warranty on the SBC unit. My car is a year past that but,he feels he can get MBZ to step up. I was under the impression the previous owner got the unit replaced two years ago but, can't confirm it now. Here is an excerpt from an email he just sent to me. I need your opinion on the proposed solution. Any feedback from you guys would be greatly appreciated:

During the testing, the SBC unit reads ok.That’s why he recommends just replacing the SBC pressure reservoir ($1761.03 before the discount)

He also noted a second option (if the unit never got replaced) to replace unit ( $2358.12 before the discount)

I’m glad you like the loaner provided continue using it at no cost until I hear back from MB or the warranty department. (Loaner is a C63 AMG!)


If they just replace the black "bomb" they would need to reset the SBC unit correct? Would that reset the "clock" back to zero actuations? Assuming I have the original SBC unit, wouldn't that be a dangerous thing to rely on the old unit for another 10 years or so? I'm thinking of biting the bullet and have the entire system replaced under warranty or my discounted cost. (This manager has provide many free services to me the past year to earn my business - like free new smart key and programming etc)Thanks again!



I have fallen in love and I'm keeping her forever.

Plutoe

Yes the programming of the new pump will automatically reset to zero.

m5zealot

Thanks! What is your opinion on just replacing the reservoir? I have heard from guys in here that the SBC unit should be able to safely operate past the expired countdown. Should I just replace the whole system for just a few hundred bucks more, or just fix what's broken (pressure reservoir) and call it a day? Again, not knowing the age of the unit in the car, I'm thinking just replace everything.

BigOldBlue

For just a few hundred dollars additional, I don't think it's a very hard decision. No question what I would do.
What kind of warranty will you get with the Complete replacement?

Aussiesuede

Since it's just a few hundred more, then definitely replace the entire unit. But since you plan on keeping the car forever, retain the old unit that's removed and replace accumulator. You're
capable of replacing the accumulator yourself, as it's very straight forward. Then when the unit fails again in the future, you'll have a spare available for your mechanic to simply install and purge.bleed the braking system.

And welcome to the "Holy Sh$T Mom, I've Got No Brakes" club. Each of us has a framed pair of the soiled shorts we were wearing when we became members of the club. As you now know, it's an experience that can not be exaggerated. The ultimate feeling of complete helplessness.

m5zealot

Thanks very much for that. I will definitely follow your suggestion. Yes, I definitely soiled a few things. I was going down a hill around 50 mph approaching a very busy intersection with no run off area. (Well there is one if I wanted to take a tumble 150 feet into the Pacific Ocean) Holy crap. Reduced braking power? Really? At that speed there is NO BRAKING except for the engine's torque. Why couldn't Mercedes come up with a visual warning the unit is going to time out in so many miles instead of this crap? I have been wrenching my 88' BMW M5 for 30 years and still trying to learn this obviously more "modern" machine.

Mercedes is stepping up and agreed to take 50% off the parts and my service manager is going to take 30% off labor even though my 2006 is a year past the extended "courtesy" warranty on the unit. They are going to throw in a new starter battery too! I love this place! I don't think any independent shop could have done this for me. Thanks for all the suggestions again.

m5zealot

The warranty is covering complete replacement but at a discounted rate only since my car is a 2006. It's very possible the previous owner had this unit replaced under the warranty but I could not verify it. Mercedes shows routine maintenance was done but couldn't find entries for the SBC replacement.

850csi

Did you guys have absolutely no ability to brake when this happened? (Isn't there supposed to be a backup system that activates the front brakes?) Was there any sort of warning that this was coming?

I am searching for an SL55, but the possibility of this sort of [potentially life-threatening] failure has me very concerned.

Das Geld 2

+1 do the brakes just fail? what was MB thinking?

Aussiesuede

When the brakes fail, the car instantly downshifts and the engine provides more initial braking effect than do the brakes. Remember, there is no master cylinder connected to the brake pedal, so the system is relying on residual built up pressure to stop the car and to say that you have 5% of capacity would seem a "optimistic" estimation. To give you an idea, after my failure, once I came to a complete stop, I thought since the brakes were holding with my foot to the floor, I could navigate another 20 feet safely by just letting the car creep forward with no throttle. Creeping just 1mph, it still took about 8 feet for the vehicle to come to a rest again. Anyone who has a genuine curiosity of just how little braking power is available can goto an open parking lot, raise the hood, disconnect the SBC wire connector from the SBC unit, and you can experience the exact braking power available.

Now for the good news. As of August 2018, it's no longer an issue to worry as much about since Mercedes has generously extended the warranty on SBC braking to 25 years unlimited mileage.

850csi

Thanks for that explanation.

I guess I'm less concerned about the cost of fixing the problem as opposed to the safety risk posed by the one-time brake failure leading up to the fix. I know that some folks get some sort of warning and therefore have an opportunity to get the relevant warranty work done, but it seems like others find out when they lose their brakes without warning.

I will say that if this was a massive safety hazard I'd expect MB to be taking more drastic measures and that we would have heard about more crashes resulting from this. Still, the near-misses on here are pretty scary.

FxFormat

You've also got your eBrake which is mechanically driven, and not hydraulics so use that to stop if you need to.

Rudeney

There is a back-up mechanical connection from the brake pedal to the "master cylinder" but it's such a small amount of physical pressure, it's worse than driving an old "land yacht" without power brakes.

850csi

850csi

Read on another board that the scary extremely weak/nonexistent brake response with no SBC assistance that some on here have experienced could be explained by improper brake flushes leaving too much air in the system, which the SBC can handle but renders the mechanical backup nearly ineffective.

It would explain why there are so many reports or 'red' failures but so few reports of actual accidents occurring as a result, and would be consistent with MB's insistence that the backup system is sufficient for safe stoppage.

I'd feel a lot better if that's true; I certainly plan on 'practicing' with SBC disconnected if I wind up with an R230.

Rudeney

I have no worries about driving mySL550 anywhere I want to go. I have AAA "platinum" which will tow up to 200 miles and I have really good insurance!

The reality is that any car can fail at any time. My parent have a new Honda CRV and the other day, it gave them a "brake system unavailable" warning and would not drive. i know that it does not use anything like SBC, but after looking at it with my father, I found that while it does use a traditional master cylinder with directly connected brake pedal, it uses an electrical pump instead of a vacuum system for power assist. I began some basic testing and found the battery was down below 11v at rest. The dealer checked and verified that low voltage was the cause of the error and replaced the batteryunder warranty. SO, it;s not just MBZ cars that have "weird electrical gremlins" these days!

m5zealot

Pretty close to me and my passenger's expression when the SBC failed at high speed down a steep hill!

m5zealot

Decide if you really love the SL 55. The SBC is a safety issue but you can get that completely replaced under the new 25 year -unlimited mile warranty from your dealer. You also need to be aware of the high cost of maintaining a 10-12 year old rolling computer with fragile parts. I paid about $26K for mine with 75K dealer serviced miles. In just over 2 years of ownership, I have spent close to $10K+ on preventive maintenance. A majority of that was replacing the failed ABC system. It's not if it will fail but when it will fail. I would budget about $20K to keep the car running for another 10+ years. Still a bargain compared to the new MSRP of an SL55! Just my 2 cents.

Rudeney

And even more of a bargain if you DIY.

850csi

I think that I have completely caught the bug and that nothing else is going to truly satisfy the itch. I'm trying to talk myself into settling for a SLK55 or a newer Mustang GT or maybe a Jag XKR but at this point I'm worried that anything else is going to leave me less than fully satisfied.

ABC doesn't bother me. After reading up I see it much the way many of you see it: an amazing system that's worth the pain if you can turn a wrench. We would have 3 unreliable old German cars, but also short commutes and the other two have been very very solid, so it's not an issue if I need to have a car up on jack stands for a week or two at a time. It also seems that the folding hardtop will run into issues but nothing too crazy.

The chance of a random BCM fire initially gave me pause. That however seems to be a very rare issue.

SBC is the only thing stopping me. I know about the warranty, but that doesn't do you any good if you have a sudden unexpected pump or electrical failure before you get any of the 'white' screens/error codes that would prompt such work, right?

And so I've been reading up on this trying to figure out the exact nature of the risk posed given the number of scary stories like yours on this and other boards/NHTSA site, bearing in mind the normal selection bias. How is this not causing more crashes? ---> Is it because such sudden unexpected failures are very rare generally speaking? Or do most find the mechanical backup to be more effective than you and some others did, for whatever reason? And are the newer replacement parts more reliable than the originals?

Aussiesuede

^^^ I wouldn't let the SBC issues be what scares you away from making a purchase since if you want certain peace of mind then it's pretty simple, just make replacing the brushes & accumulator in the SBC motor a part of your normal expected maintenance routine. Replace them both every 3 years just so you never have to worry about an unexpected failure. All it requires is an investment of $2 for carbon brushes, and $100 for the accumulator , and an afternoon of your time. Every three years is definitely overkill, but at least you'd have guaranteed peace of mind.

alk247

Sounds like relatively low cost and reasonable thing to do, but I am not sure if doing such repair would void Benz's 25 year SBC warranty?

Rudeney

Honestly, I think you are worrying about a problem that is less likely to happen than being hit by a dump truck. SBC generally does not spontaneously fail. You usually get warnings beforehand. Of course anything mechanical can always fail, but you don't hear much about it happening with SBC.

Zayne du Bery

I recently got an error "Reduced Breaking Power. Start Engine." After having the car diagnosed with a Bosch tool the origin was that of the SBC Unit. One part in particular - Pressure Accumilator. It is said that the SBC Unit cannot be fixed but the guys at Automia recon they can... for R15000. Any suggestions?

Rudeney

For us in the USA, the SBC warranty was extended to 25 years, no mileage or ownership limitations. Maybe your country has something, too? it might be worth checking with a dealer or the MBZ corporate office in your country.