Growling Noise on E320. Brake system?

[ArleighKerr]

I’ve got an ’04 E320 wagon that makes an awful growling noise when the car starts up (an occasionally while driving). The noise started soon after getting the car back from the repair shop after a really bad accident damaging the front end.

Naturally, noise doesn’t happen every time, but it does it enough so that the Mercedes mechanics have heard it themselves. Sometimes it happens the moment the engine starts, sometimes after brake pedal is depressed and car is shifted into gear. Sometimes happens while driving slowly through. Never happens while driving on the freeway.

Noise lasts 5-10 seconds and is extremely loud. Read another posting here about a MBUSA service bulletin mentioning “noises associated with SBC system” and “buzzing noise during pressure buildup from SBC system” Could be this. One man’s buzz might be another man’s growl.

It’s been to the dealer twice with no resolution. They do not believe it was caused by the accident and are dealing with it as a warranty problem. They replaced the SBC brake unit, added insulation, checked all the hoses to make sure they were clean and unblocked. They say the computer reports no “error code” that would indicate a known problem. They kept the car for 7 days during the last visit and proclaimed the car fixed. Drove home fine, but then growled next time we started up the car.

Arleigh Kerr
Seattle, WA
arleighkerr@qwest.net
2004 SLK320 (mine)
2004 E320 (wife’s)

[lkchris]

Our new one has done it once or twice.

Usually before starting engine.

Usually just gurgleing, but once or twice a growl/groan.

I, too, think it's SBC.

[Bela]

The MB mechanics are certainly in a position to do the best diagnosis, but I thought I'd mention that mine makes a noise on opening the door, which I understand is the self-leveling suspension. It's not a problem though. Most likely yours has a different cause, but if it involves the startup period, I would check any of the pumps. Might be low fluid in the power steering, for instance.

Bela

[lkchris]

Actually, I think the SBC brake system "gets ready" as soon as door is opened.

[mgburg]

Have an AC technician check the charge level on the system and be sure it's properly balanced - before AC engagement (First thing in the morning, everything cold and at static pressure w/everything turned off, engine included) - and when the system is operating - the proper High Pressure for the conditions of the day (Humidity levels-ambient tempertures, etc....) and at the same time the Low Pressure side should be in the proper range for like conditions. If the system has too much coolant, then the compressor will be overloaded and the "growling" is the drag that the belt is putting on the pulley as the clutch is engaging...that's another possibilty. Your service technician might have been a little too "helpful" and just "touched up" your system for you. (Yeah, right! Nothing's for free anymore! :D )

I just experienced a similiar "sound" w/my S-10...turned out that the garage-monkey added about 6oz. of R-134a...when I started the engine in the morning, this system "engages" the clutch every so-often (apparently this helps in keeping the seals fresh during the winter) even when AC isn't being called for. I ended up "bleeding" a little of the R-134a "off" to the point where the "growling" quit. Everything else checked out fine. This S-10 has 189K on her and she's only an '00! :D

[lkchris]

Have an AC technician check the charge level

Is this a response to the question at hand?

How does "opening a door" cause noise in the air conditioning?

Chevy S-10 experience is quite unlikely analogous to anything Mercedes IMHO.

[mgburg]

Kent:

I was referencing ArleighKerr's post (#1), not Bela's post (#3). :(

I was "throwing" that out there ... our AC doesn't work on our MB (yet). I'm seriously thinking about having it recharged w/the original formula R12 and not converting it over to R134a.

If/when I do do it, it will be In some other state. Wisconsin has "killer" regs - they won't let a "layperson" even buy R134a! You can only imagine what "limbs" the "tree-huggers" will rip off you if you're found w/a can of R-12 and no "license" to dispense! If you want the R134a brand of coolant, you have to go across the river (Mississippi) to get a can from the local WAL*MART or K-Mart. :o

[DieselDave]

I understand what ArleighKerr is referring to. My 2005 E320cdi "charges" the brake system from time to time and makes a sound that qualifies as described.

[Bela]

Arleigh, let us know what you finally determine to be the cause. This is a bit like a mystery story, and it's always nice to find out who is the culprit.

Bela

[ArleighKerr]

Yes, I’ll let you all know the outcome. We are familiar with the noise caused by the brake system charging; it’s done that since the day we bought the car. Mercedes techs assured us back then that it’s normal. Recently they confirmed what other posters have said that merely opening a door can cause the brake system to charge – the car knows it’s going to be used, so it’s getting ready. But the growling noise we are now hearing is many times louder and longer in duration than the charging noise.

We are now getting the loud growl while driving around city streets at 30-40 mph and while sitting at stops while the brake pedal is depressed.

Thanks to all to have given their advice, I’m going to print out this thread and give it to the mechanics.

Arleigh

[barnesdh]

I experience the same 'growling' noise with my '04 E320 4Matic sedan. I assumed it was a normal noise associated with the SBC system. This noise has been occurring since I bought it new. It did not concern me until I read these posts. The brakes have been working perfectly....especially since the SBC recall/software upgrades. My car is due for a normal 20k service soon. I will put it on the list for the dealer to check. I will report their findings/comments to this forum.

Dave

[Drivbiwire]

Its caused by the SBC performing an autotest and pressure check of the system. This is why they require you to de-activate the system when changing the brake pads and discs.

The following may cause pressure to build up automatically
• Opening a door
• Operating the central locking system
• turning the key to position 1
• Depressing the brake pedal
• Opening the trunk
• operating the parking brake

SBC is functional as soon as it is “wakened” by:
• opening a door (via CAN)
• operating the central locking system (via CAN)
• depressing the brake pedal
• turning key to position 1
• operating parking brake
•The Wake-Up may be followed by a Pre-Drive self
Check performed by SBC

When SBC performs a PDC after a "wake-up", the following are
checked:
Warning! Pressure is applied to brake calipers (~60 bar)
• reservoir pressure (if low, it will be corrected by running the
high pressure charge pump in the hydraulic unit)
• pressure sensors
• control valves
• leak tests
• operational checks
Note: self-tests are constantly conducted during driving (~ once every 16
brake applications)

Time that SBC remains operational after use:
• with vehicle stationary and was locked = 20 seconds
• with vehicle stationary and ignition in “0”,
brake pedal not operated = 2 minutes
• with vehicle stationary, ignition in “0”,
brake pedal operated in delayed off phase and
released again = 4 minutes




The SBC system during the self check applies approx 60bar of pressure to all four pads to verify integrity of the brake system. This also occurs after so many cycles or depressions of the brake pedal with vehicle at a complete stop, however with the engine running it is often not noticed by the driver. This self check also serves to charge the black pressure accumulator mounted below the SBC drive motor to keep brake pressure ready for an emergency braking situation.

http://mbca.cartama.net/attachment.php?attachmentid=3578&stc=1

Normal, absolutely + mandatory!

DB

[barnesdh]

Drivebywire.....
Your response re this thread is nothing short of outstanding. On behalf of all of us who had an interest to know...thanks a whole bunch!!!! You can fly me anywhere.

Dave

[barnesdh]

Drivbiwire...
Please accept my apology for butchering the spelling of your user name. Some of us mechanical engineers never learned to spell good.

Dave

[ArleighKerr]

It was the 'rear leveler pump'. Took 'em forever, but they finally discovered the problem. First the replaced the bracket hold the pump and that helped a little, but finally replaced the pump itself and that fixed it. It's been two months since it was replaced and we've been growl-free.