bkdc

For the past two weeks I noticed a mild hissing white noise when I start my car. It seems to be decrease after 10 minutes of driving but it does not disappear. It is a mild hissing noise coming from the speakers located on the back of the front passenger seat. Hissing continues after I turn off my engine until the remaining electronics turn off minutes later. Changing the sound settings don’t affect it.

I have the Burmester 3D system. Anyone have any experience with this? Given that it should be silent, I’m wondering whether there is a electrical harness problem

schack

I also have the Burmester 3-D system. I didn’t realize there were speakers in the backs of the front seats. I thought they were vents for the cooled seats. My system does not make the hissing noise.

Katie22

How about a leaking air line for the seat air bladder system?

MBNUT1

Turn the Audio system off and see if it goes away.

bkdc

this is a better answer.

MBS63AMG

Are the cooling fans of the passenger seat on? Are the cooling fans of the rear passenger on?

bkdc

Not the cooling fans. I think Katie22 is correct. Anyone have the diagrams on the very complicated seat? I saw a YouTube video on a W221 air bladder repair. I’ll try my hand at it. Car is still under CPO extended warranty but I don’t think the air bladder system is included.

badq45t

I wouldn't assume the CPO warranty doesn't cover that, worthwhile to check with a service writer. I have not seen anything so far that my CPO warranty didn't cover, scored a Flexplate last service and the housing around my electric plug (I have a S550e) was covered.

bkdc

I immediately found the leak when I took the seat panel off. Purple hose at the bottom. The pneumatic hose cracked at the fitting because the nylon? Hose was clearly too short and under constant tension. I tried to splice a PVC hose with brass barbed fitting but the 3/16 inch ID brass barb splicer was too large and split the nylon hose as the hose had minimal flexibility. I didn’t want to try a 1/8 inch ID brass barb splicer at the risk of increasing the resistance and demand on the pump (Poiseulle’s equation) as this being the widest hose may be directly coming out of the pump.. I was thinking of buying a push-snap pneumatic fittingly I can find the matching size.

Does anyone know where I can buy this purple size hose or buy pneumatic hoses which are not only even sized (6, 8, 10mm)? It doesn’t have to be purple obviously. I was having trouble finding a nylon 7mm. It is larger than all the other pneumatic hoses in the back of the seat panel which appear to be 6mm OD. This purple one is somewhere in the 6.6 to 6.9mm OD range depending on where I measure. Maybe it’s a 7mm? I could not find a online site selling 7mm nylon tubing.

bkdc

Hissing leak fixed. I spliced in a 1/4” outer diameter pneumatic tube by using a 1/4” OD push connector. It was a tight fit around the purple tube but it worked. The existing tube attachment was reused.

New problem. I can’t change my seat bolster settings. There is no leak in the air bladders. However, I cannot return them to original settings. I cannot firm up, nor can I deflate and soften from the existing settings on the shoulder, lumbar or side cushions. They remain nice and inflated but will not change from their existing settings. Nor can I activate the massage function. This issue existed before my tube leak but I wrote them off to the leaking tube which has definitely been repaired.

Anyone have an idea? Or does it need some kind of Mercedes STAR system software reset?

konigstiger

Quick check f421 (30A) & f490 (5A) @ rear fuse panel.

bkdc

Fuses are ok. I have a cheap Foxwell OBD2 reader with no codes. I’ll check later on the OBDLink MX+, and if nothing shows up, I think it’s probably a Mercedes STAR diagnostic system reset.

bkdc

Problem solved. It merely required the manufacturer specific error codes to be cleared. I used a Autel MaxiCOM to read and clear all the codes. Everything now functions perfectly.