05 CDI SBC brake replacement - PeachParts Mercedes-Benz Forum

spark3542 · #1 10-15-2015, 12:18 PM

There is not a lot of discussion about the SBC brake units on 05 and 06 CDIs, and I recently had issued with mine, so I'll update the group with what happened.

I was out on a test drive (for a fuel issue I was chasing), I inadvertently hit a hard pothole, and heard an excessively loud clunk in the front right suspension. It drove OK immediately after, so I wasn't overly concerned.

About a mile later, under normal driving conditions, I got the red dash of death...more specifically "Reduced braking power...stop immediately" etc. The braking power was very severely reduced...step hard on the pedal, and the car slows down gradually. I'd bee in dire straits if I needed a panic stop.

I was about 5 miles from home, and decided not to stop (pardon the irony) and continue to get the car back to my home to assess the situation. The drive home consisted of loud beeping, changing panic info on dash, and car would not shift beyond 2nd gear.

At home I disconnected the SBC connector and reconnected, and red dash went away, and brakes felt normal.

I assumed since the red dash came on once, it will come on again, and severely reduced braking power is unsettling.

I ordered SBC unit from online MB (about $980 but $150 core charge, so net of $830). There are at least 4 different SBC units (for different platforms) so I needed to supply my VIN for the correct one. What I didn't know it that it also needs programming after installation.

I installed the unit, bled the calipers using the Motive Power Bleeder (model 0109 is the right one for the CDI). First time using that power bleeder, and it's awesome.

Without programming though, you get nothing. Red light immediately, and it will let you start the car, but not move it out of Park, so I can't even have it towed to someone to have it programmed.

I end up putting the old unit back in, bleed the lines again, and hope for no red dash. No red dash, and drove cautiously to a local indy that has MB programming tools. They installed new unit, bled and programmed it ($527 later) I'm good to go.

What I learned is that the SBC is truly brake by wire...under normal operation you are using none of your foot to move hydraulic fluid to a caliper. Sensors measuring brake pedal application position and rate is what is telling the SBC unit to send fluid and at what pressure to which wheels. The master cylinder is only emergency (and doesn't do a very good job of it).

I also learned if your car doesn't want to move, it will not let you go out of park, no matter what you try!

I do all my own work, so It's frustrating being at the mercy of others since I don't have the $40,000 programming equipment.

And I have no idea if the hard pothole contributed to the SBC unit failing of not, just a data point I have.

...but I still love my CDI

shertex · #2 10-15-2015, 02:42 PM

Thanks for the overview… Sorry to hear about your difficulties. How many miles on the car if I may ask?

Oops...never mind....I see 256k.

NH82W123 · #3 10-15-2015, 02:51 PM

Thanks for that run-down, Mark.

I expect I'll be in your shoes before long. My 05 has the original SBC unit with over 130K miles on it. The unit makes loud noises while driving or even when just getting into the car. And I've gotten a few "brake - visit workshop" notifications (not the red dash of death, more like a courteous suggestion) that have gone away on their own.

hangit · #4 10-15-2015, 06:18 PM

Please file your experience with the NHTSA. Here is the link to another forum where you can do some more reading.

SBC and NHTSA - Mercedes-Benz Forum

John

chronometers · #5 10-16-2015, 11:37 PM

Quote:

Originally Posted by spark3542

There is not a lot of discussion about the SBC brake units on 05 and 06 CDIs, and I recently had issued with mine, so I'll update the group with what happened.

I was out on a test drive (for a fuel issue I was chasing), I inadvertently hit a hard pothole, and heard an excessively loud clunk in the front right suspension. It drove OK immediately after, so I wasn't overly concerned.

About a mile later, under normal driving conditions, I got the red dash of death...more specifically "Reduced braking power...stop immediately" etc. The braking power was very severely reduced...step hard on the pedal, and the car slows down gradually. I'd bee in dire straits if I needed a panic stop.

I was about 5 miles from home, and decided not to stop (pardon the irony) and continue to get the car back to my home to assess the situation. The drive home consisted of loud beeping, changing panic info on dash, and car would not shift beyond 2nd gear.

At home I disconnected the SBC connector and reconnected, and red dash went away, and brakes felt normal.

I assumed since the red dash came on once, it will come on again, and severely reduced braking power is unsettling.

I ordered SBC unit from online MB (about $980 but $150 core charge, so net of $830). There are at least 4 different SBC units (for different platforms) so I needed to supply my VIN for the correct one. What I didn't know it that it also needs programming after installation.

I installed the unit, bled the calipers using the Motive Power Bleeder (model 0109 is the right one for the CDI). First time using that power bleeder, and it's awesome.

Without programming though, you get nothing. Red light immediately, and it will let you start the car, but not move it out of Park, so I can't even have it towed to someone to have it programmed.

I end up putting the old unit back in, bleed the lines again, and hope for no red dash. No red dash, and drove cautiously to a local indy that has MB programming tools. They installed new unit, bled and programmed it ($527 later) I'm good to go.

What I learned is that the SBC is truly brake by wire...under normal operation you are using none of your foot to move hydraulic fluid to a caliper. Sensors measuring brake pedal application position and rate is what is telling the SBC unit to send fluid and at what pressure to which wheels. The master cylinder is only emergency (and doesn't do a very good job of it).

I also learned if your car doesn't want to move, it will not let you go out of park, no matter what you try!

I do all my own work, so It's frustrating being at the mercy of others since I don't have the $40,000 programming equipment.

And I have no idea if the hard pothole contributed to the SBC unit failing of not, just a data point I have.

...but I still love my CDI

Did you have any warnings about service, etc. prior to the failure warning? This is a real weak point with the SBC equipped cars if there is no warning prior to failure.

spark3542 · #6 10-19-2015, 12:31 PM

Quote:

Originally Posted by chronometers

Did you have any warnings about service, etc. prior to the failure warning? This is a real weak point with the SBC equipped cars if there is no warning prior to failure.

I had no prior warnings whatsoever.

Also, I do all my own work, so pads/rotor work was always done with just disconnecting the SBC connector and reconnecting when through.

chronometers · #7 10-20-2015, 10:57 AM

Wow....that does indeed sound like a critical design flaw. I am surprised the system (vehicle primary braking) could fail without warning.

Your's is not an isolated incident.