Leej

This morning, I started my the car (2008 SL550, 66,000 miles) and I drove about 150 yards, I got a "BRAKE" warning, then red "ABS, ESP inoperable warning." It then felt like I only had about 10% on the brakes, had to really push the brake pedal the floor to get anything (very unnerving, and I was happy I wasn't going very fast). Then I got the "STOP" sign on the dash, and the "Reduced Brake Effect Depress brake fully" warning (and I think it was making a chiming noise as well). Also, felt like the car had less power (maybe limp mode), but with everything going on, maybe was just being overly cautious... Luckily there wasn't any traffic and I got back home safely (only a block or two).

I turned the car off and looked for any major issues, but didn't see anything. I started the car again, and all the warnings came back. I checked the codes with a cheap ODB reader, and I had NO codes (I don't have STAR diagnostic, but it probably would help in this issue) but warnings were still there. I started the car and let it run a few minutes, but warning lights were still there. Finally I left the car, and drove my other car to work.

I immediately assumed the SBC was failing, and hopefully it would be covered under warranty (however I am 1.5 hours from the nearest Dealer). But with further reading online, I thought (hopefully) that maybe the battery voltage was just low. I did recall that I turned the seat heater on a few seconds before all the red warnings started, and I had not started the car in a couple of days (maybe 3). But I didn't not notice any battery voltage warnings.

I came home this afternoon, and checked the rear battery voltage with a meter, and got 11.7 volts (kind of low, right?). I started the car and everything was fine, no warning lights or anything (I did NOT turn on the seat heater). Charging voltage (with car running) was about 14.1 V (I think that is pretty good, right?).

Is it possible that the battery voltage was slightly low from sitting (or age, or the battery is going bad), and the pull from the seat heater caused it to be low enough that the SBC pump could not built up enough pressure and shut down??? Or maybe I have a battery that is going bad (I've only had the car for a couple of months, and I couldn't find a date code on the battery)? I do have a CTEK battery tender, so I hooked it up and will let it charge.

Is all this voltage stuff just wishful thinking and hoping its not the SBC? I presume STAR would tell me for sure, but I don't have STAR. As I understand it, if it is the SBC, it is under warranty, but I'm 90 miles from the nearest dealer.

Any thoughts? I could do some testing on the battery? But, I really don't want to simply charge up the battery and drive it to see if my brake booster stops working again... Any thoughts or advice would be appreciated.

Thanks

Lee
2008 SL550

bobterry99

The voltages you measured are fine.

What occurred may be a one time event that happened for no apparent reason and does not repeat itself. I would drive the car.

kbob999

It sounds like the SBC pump was not working, and that is why the brakes went to 10% or normal.

The question is...why did the pump stop working? Could be low battery; the SBC reservoir failing; a temporary failure of the SBC pump; or a random electrical fault.
You really need to pull SDS codes, as they will show faults that occurred, then are no longer current. I'd suggest a trip to the local independent MB who has an SDS to work with.

I've had similar warnings, but not the brakes going away. This was attributed to the alternator failing. Does not sound like a bad alternator as your voltage looks good when running.
If you don't have a battery maintainer on the rear battery, you should get one for any storage longer than 3 days.

Keep us posted on the outcome of your issue.

Rudeney

Generally, if this is a battery problem, you get a battery icon on the MFD and various consumers (steering wheel adjustment, heated seats, vario roof, etc.) will be disabled. I think you had an SBC failure. I'd pull codes, and has you have found a generic OBDII scanner won't do it. If you don't want to invest in SDS< an alternative would be the iCarsoft MBII or the Autel MD802 Elite. It can read codes from all the car's systems. If the code does show an SBC fault, I'd contact the dealer to setup a repair appointment. It is now covered under warranty for 25 years, unlimited mileage, any current owner.

Leej

Thanks for the all the advice.

I did not get any battery related warnings or "convenience functions temporarily unavailable" messages, but the car had been sitting for a couple of days, and it happened a few seconds after turning on the seat heater... I will try to investigate the battery a little more just to rule that out. If I can find a date code that indicated it was older than 3 years, I might just replace it for good measure.

I really want (and probably need) to invest in SDS, and maybe this will be good motivation. ICarsoft and MD802 seem to be less than $200, but a SDS with used laptop seems to be around $550 to $650. I'll see if any of the independent shops here have ability to check those codes.

I'll post results here, but I have a feeling it will take some time to get resolved (especially if I am replacing SBC)...

THANKS again.

Lee

bobterry99

Once the engine is started the alternator powers the vehicle electrical system. Only under extraordinary circumstances could the battery be an issue.

A Dell D630 laptop with no hard drive is about $60 on eBay. The SDS multiplexer, cable, and a hard drive with the software are about $275 from a variety of vendors on aliexpress.com.

Leej

I have had a battery maintenance charger on the car for 2 days now, and the voltage measures 12.1 V (while still not running, but still connected in the car), I really thought it would have been little higher? I haven't driven the car, everything seems fine (no warning lights)??? The front (starter) battery was replaced a few months ago right before I bought the car. If the rear battery was bad or going bad, would the front battery help to maintain the rear battery, or at least affect the voltage measurement?

SDS has been ordered. Thanks for the advice.

Lee

Rudeney

The front/start battery will be switched in to supplement the rear/consumer battery, but I think it has to get below a threshold of something like 9.8v. Below are some docs from WIS (which you will have with your coming SDS setup) that describe it. The first one,which is through MY2008, does not mention the voltages and stages like it does in the MY2009+ doc, but I think they are similar. Bobterry may be able to clarify/refute/support that.

http://benzbits.com/r230/BatterySystem.pdf
http://benzbits.com/r230/BatterySystem2009.pdf

bobterry99

If the rear battery were the only battery, I still would not be concerned about it. If you are getting no warning message stating "consumers offline" or the like, then your rear battery is fine.

The starter battery has no effect on your rear battery voltage measurement.

Rudeney

Just a note about the "consumers offline" messages...I think these were disabled by default after a certain model year. I'm not sure when, but on m MY2011, there are no messages on the MFD, but they do still get cut-off when the consumer battery voltage is low.

Frederick NL

Leej

Update, I finally received SDS and got it up and running with some help from seller (connection is still a little quirky, but I adjust baud rate and hope it is more stable - that's another topic...)..

I have pulled codes, and there were a lot of codes, most relating to other things (i.e. (Dr/Pass/Rear SaM, Sat Radio antenna cable (maybe that's why satellite won't connect, etc.). None of the codes (other than SBC) seemed critical and I will sort as time permits.

Regarding the SBC codes:
C25D4: Hydraulic fault: No or insufficient pressure supply
C26DE: Hydraulic fault: Malfunction in pressure supply
C26BB: Hydraulic fault: Malfunction in pressure supply

I have not starting diagnosing these yet, but it looks like SBC pump timed out without building enough pressure for some unknown reason and shut down. It has been working since. Could be air in lines, or could be worn out pump???

Also in "Reading out ring memory":
C25D4: Hydraulic fault: No or insufficient pressure supply
C25D5: Hydraulic fault: Malfunction in pressure supply
(repeat) C25D4: Hydraulic fault: No or insufficient pressure supply

Nearest Dealer is an hour and a half away, but might be worth taking to Dealer and have them evaluate SBC for warranty replacement...

I'll continue to look into these codes, and suggestions would be appreciated.

Thanks

Lee

kbob999

Lee,
Good for you on the SDS purchase.
Any item with 'f' fault happened in the past, is not active, and can be cleared to see if it returns. Most do not. Any 'F' fault is current and happening now.

Sounds like the motor in the SBC unit quit working, or you have a massive leak of brake fluid, which should be obvious.

The SBC motor (electric pump) won't quit working when it reaches the actuation limit, only when the motor, or part of the system quits or breaks.
The motor is one of the noises you hear when you open the door and 'wake up' the car.
If it does not have pressure, or inadequate pressure, the warning will occur. In your case you received no brake assist, so the SBC pressure is basically zero.

Could be a fuse to the system, not supplying power, but my guess is the SBC motor has quit and you get a free replacement from MB. See if you can hear the pump motor run when you wake up the car.
You may be able to run the motor manually in 'Actuation' portion of the SDS.

Leej

@kbob999
Thanks for the reply and advice. The pump is working now, and it wakes up as suspected. This was a one time event that occurred once in the morning, and by the afternoon after sitting, it was fine (no lights and SBC pump running again)??? However, I haven't been driving the car much since this originally occurred (2 weeks ago, Jan 14) due to nasty weather here (cold/ice/salty roads), but I have driven it five or six times since occurrence with no issues...

I will further investigate some of the easier remedies/tests in SDS for these codes and see if anything obvious jumps out, but I will likely clear it and see if it returns, pending any other advice.

Ultimately, I probably take it to Dealership and hope to get SBC replacement under warranty (but nearest dealer is 1.5 hours away, and will require two trips, scheduling, etc...)...

Thanks again, and please let me know if anyone has any other thoughts or suggestions.

Lee
2008 SL550

Leej

I have had no other brake issues, and no other warning lights since this issue started 2 months ago. However, I did take the car to the Dealership earlier this week, and they said the passenger side SAM was defective and needed to be replaced ($710). They also saw the stored codes for the SBC pump (posted above in my previous post), and they replaced the SBC pump under warranty and flushed brake fluid, etc. They said they were very aware of the SBC issues and warranty and there was no issue at all!

I guess it is possible that the defective SAM could be related to the brake/SBC issues, but both the SAM and SBC are replaced now and all is good! Was glad SBC was under warranty!

Thanks

Lee