ethanjean

Hey guys I need some help with a brake flush on an 05 R230. I was bleeding my brakes using a mitey vac. I wasn't paying attention and didn't fill the reservoir in time and got air in the system. Immediately after, with the engine off and stepping on the brake, I got a RED "Reduce Braking effect start engine".


I ended up getting a Motive pump power bleeder and re-bled the brakes with about 2 liters of fluid. But I'm still getting the brake error. I'm assuming air got into the abs something. Any other place I can try to bleed air out of the system.


The brake pump still kicks in when you open and close the door and the brakes were fine before my goofed up bleed. Help please anyone.

vtvette

Do you see any air bubbles in the fluid at the calipers?

ethanjean

There were some bubbles but not that much. I bled all the calipers several times after with the equivalent of 3 liters of fluid. It is running clear and no bubbles but I think air got pulled into the sbc valve. Just not sure if there was something else I could try before bringing it in to shop to power bleed it through star as someone suggested.

vtvette

Either you do still have air in the sbc valve as you suspect or, it's possible you have cleared the air that was detected out when you flushed the system with the 3 liters but the code remains and needs to be cleared.

If the brakes feel normal now the only thing I can think you *may* try is:

Disconnect the large connector in the front of the sbc module for a few minutes and see if this resets the module/code? From research I did on this forum I disconnected this connector before when replacing my brake pads. Much quicker than hooking up my Star and putting the brakes in Service Mode. I did not disconnect either batteries. Don't turn on the ignition while the module is disconnected and you will have no issues. I'm thinking when you reconnect the module it may run a self diagnostic and realize the brakes are fine?

If the above doesn't work follow procedure and disconnect the batteries for a little while and see if it clears the code. Once you hook the batteries back up and the car sees the brake system is functioning properly it *may* clear the error code? I don't know what is considered hard and soft codes with the R230. These are sorta long shots I know but other than that I don't know how you'll get the code cleared without Star.

Please post a follow up it will be interesting to hear how this turns out.

cal1

Just wanted to add, it would not be a bad idea to make sure the key or keyless is nowhere near the car and don't open any doors during the disconnect/connect procedure.

cal1

By the way, I doubt you would ever feel the typical mushy brakes associated with air in the lines because SBC is essentially electronic or "brake by wire."

vtvette

Great point about not having the key nearby thanks for mentioning.

Interesting question about not feeling the mushy feel typical of a "normal" brake system. I wonder if SBC can somehow compensate for pedal feel if air gets in a brake line? It is electronic between the pedal and the module but, conventional hydraulics between the module and the calipers (at least that's my understanding of the system. Never actually serviced mine).

cal1

I'm not real sure. From looking at the diagram, it appears to me because we are pushing on a "travel simulator" it makes me think it is something like a potentiometer that could be sending a control signal to the SBC unit. It takes that signal plus tons of other data from sensors on the car and decides how much hyd pressure to apply to each brake. I know SBC can and does apply braking pressure at different rates to different brakes depending upon conditions.




I have been on an SBC kick lately so apologies to those that have seen the diagram a thousand times.

vtvette

Nice Cal1 thanks for posting the diagram. It looks like the system does have a hydraulic backup to the pedal in case the system fails.

cal1

Yeah it does, but only to the front brakes. I have read lots about significantly reduced braking in the event of an SBC failure.

ethanjean

Really appreciate the diagram! Helped me to understand things. Car is at the shop. I will update this post after I figure out whats wrong. Basically there seems to be air in the SBC/abs system from my failed flush that is preventing the system from getting full pressure. Constant red error...

When this happens the SBC switches valves and falls back to the tiny master cylinder and the brakes feel like it has less than 1/5 of the normal stopping power.

I was also having issues where it seemed like the SBC got to the correct pressure, but when you hit the brake, the petal just hits the floor with no resistance. When this happened there was no fall over to the master cylinder and the brakes didn't function at all. This only occurred during start up, but very scary.

cal1

Please do report back. What you describe sounds very much like the SBC failures I have read about in various places on the net. It sounds like your issue will be easily resolved with a purge of the air and a reset to SBC.

I think unrelated to your issue, but a number of people have been dealing with the SBC "service Threshold reached". I have been on a mission to shed as much light on the subject as possible. Some people are choosing to reset the SBC counter either through STAR/DAS Xentry or purchasing a cheap dongle that plugs into OBD2. My SL hit the service threshold and I decided to replace SBC with a rebuilt unit. It is a big job for home mech's, at least too big for me so I popped for the 2k to have the dealer do the job.

Although I recommend replacing the SBC unit if it has reached it's preassigned service threshold, I am trying to provide to all members as much accurate information as possible to help them make there own decision. Some people seem to think the hydraulic back up system can safely stop the car under most conditions. I tend to think the opposite is true. I had always believed they could expect to push the pedal nearly to the floor and braking will still be reduced greatly. The diagram suggests this and you reported exactly what I would have expected based on it.

Good luck with your situation.

vtvette

Cal1 at what point did you receive the "service threshold reached" message on your SL? My 2005 SL55 has 110,000 miles. Do you know what parameters trigger the message? Is it mileage, age or other factors?

Thanks.

cal1

I have a 03 and got the message late last fall, a few days before I put the car to bed for winter. The car had about 97,000 on it. The majority of the stuff I read on the net suggests there is a counter that counts brake actuations. I am guessing just a tap of the brake counts. The threshold appears to be 300,000 actuations. I think most people are seeing this somewhere around 100,000 + miles, but driving style and freeway vs local driving could make for a big range.

I have also heard the counter can be read in DAS/Xenty. I looked today briefly and did not find it.

latemodel21

My understanding is the parameter is purely the "count"

On my 2003 SL55, I got the message at approx 75,000 (at 10 years and 3 months). Curiously, I work with someone who has a 2004 SL500 that has over 150,000 miles and has NOT gotten the message yet.

you can read the "count" with the star tester (and reset it if you dare).

Cheers,
Chris

ethanjean

Unfortunately, my SBC had to be replaced. My mechanic did his best to avoid it by trying a new accumulator first. That helped but ultimately the SBC was not maintaing enough pressure. My 05 SL55 has less than 50k, so we didn't think it was the SBC. STAR reported that 3 valves were stuck and SBC could not maintain pressure. The working theory is that the bad bleed and air being pulled into the SBC (possibly loosened some additional particulates) caused some particles to be lodged into the valves preventing them from closing 100%. This made sense to me for 2 reasons.

1. When I was doing the initial bleed the fluid was not that dark, but I did notice a some particles in the fluid, not a lot but more than I expected and bigger than I expected.

2. The new SBC is really quiet. I barely notice it turn on when I open the door now and when I do hear it it doesn't stay on for long (1s Buzz). Prior to this, there was an obvious distinct motor/pumping sound for 1-2s everytime I opened and closed the door etc.

The old SBC valves may have already had a tiny leak + old accumulator causing the pump to come on more often to maintain the correct pressure. The flush prob just put the nail in the coffin with the extra particles.

Even if the pump motor was working perfectly, the valves are encased in the block so there was no way to avoid replacing it. They spent days bleeding it multiple times hoping to clear it out, but to no success.

Prior to this I did not think there was anything wrong with the vehicle. If I had done the flush correctly my sbc probably would have chugged along for another 25-50k miles. But who knows for sure...

An FYI for the next guy... When The brake reservoir is 20-25% full, it is basically already empty and pulling in AIR.

cal1

Bad news, but at least it is now fixed. I know of a few guys that had SBC fail because of issues similar to yours. Seems to me it is rare though.

When I was doing research on SBC, I seem to recall reading how Bosch and MB had worked together on the SBC system. They had expectations that many high end cars like Audi, BMW and others would adopt the system. Bosch would be able to make more and reduce the per unit cost. Unfortunately, it didn't work out that way.

ethanjean

It is also my understanding that the service limit is 300,000 actuations. But I don't know if that is the number of pedal presses or SBC motor actuations or even something else.

If it is motor actuations then a small leak like I may have had in my SBC, would increase the number of actuations. Eg. I have noticed the SBC kick in when at a stop light for example.

I've seen some obd adapters designed to reset this limit and I also read that star allows you to hit the reset on actuations as part of the SBC replacement process. But you run the risk of sudden brake failure. From my experience driving with the hydraulic backup, it is scary...

cal1

I have certainly come across many discussions on the net all stating 300,000 actuations. What constitutes an actuation was never made completely clear to me.

I have looked in my Xentry/Das/Star system and could not find where to reset the counter, but have also heard it can be done. I am no pro with my DAS system. I have seen OBD dongles or adapters that allow one to reset. Most have options of 25%, 50%, 75% or 100% reset.

I drove my SL around for about a month with the white SBC warning light on figuring that MB/Bosch built in a cushion on the service threshold. I found myself driving the 500+ HP car like a grandmother since I never knew when or if I was going to get the red SBC failure indicator.