leonelalbarran

I have a pop/thump noise coming from the rear of my C230 Sport w/ auto trans when I am at a complete stop with the brakes applied and in drive. For example at a stop light or a drive thru. It starts with a soft noise like a click then 2-3 seconds later a very rapid series of thumps/pops happens then it goes away until I come to a complete stop again with the car in drive and the brakes are applied. MB technicians can't figure it out after $1200 in diagnosing fees. Hence the title of my post. I am new to the MB world so any help would be very MUCH appreciated!

tee

Canister shut off valve or purge valve up against the body.

Carsy

I get a loud "grumble" type sound sometimes when light breaking & when almost stopped . It is pretty normal & caused by pad vibration . I think a pad grease may fix it but I have never bothered.

Try doing it with someone else driving with you standing beside or running beside the car. You may be able to pinpoint the location. I have to do this sometimes to find which disc stone guard has a stone underneath it !!

leonelalbarran

Thank you guys for the input. I really appreciate it. Tee, have you had the same issue and did you fix it by working on the parts you mentioned? Carsy, thank you for replying but my issue occurs when I am at a complete stop with the brakes applied to keep the car at a stand still

leonelalbarran

Did you have same issue and is that how you fixed it? Could you tell me a little more?

tee

Look at the purge valve it is located by the left front head light start the car and when you hear/ feel the thumping see if it matches the purge valve. Very common that people complain about this you can insulate it from the body better with felt tape and that seems to help. If it is the canister shut off they make more of a popping type sound from the r/r of car.

Glyn M Ruck

EECS Purge valve.



Also twin fuel level sensors under the back seat can make strange knocking noises.

tee

Never seen the fuel sensors make noises but lots of purge valve noises.

Glyn M Ruck

You will find a thread by LILBENZ (Matt) IIRC where we discuss noisy fuel level sensors.

tee

I'm not doubting you just saying I have never seen fuel senders make a thumping noise

BF_JC230

[QUOTE=leonelalbarran;5944536] MB technicians can't figure it out after $1200 in diagnosing fees. QUOTE]

Did you pay them $1,200 for nothing?...Did they take $1,200 for no work rendered/issue resolved?

leonelalbarran

They connected the OBDII machine. Took a look at the car. Lifted it up and looked underneath. I mean they have tried but after 3 attempts of looking with no results is just hard to believe lol.

leonelalbarran

Thank you all for the replies. Quick question for you tee, would this sort of thing not throw a code? That is one thing I forgot to mention in my original post. The computer is not throwing any codes....

tee

It will not throw a code because the valve is working. You could unplug the purge valve and drive it to see if the noise is gone but doing this will store a code.

Holmes5518

Sounds to me like you are describing the tapping of the charcoal canister. They are loud on 203 sedans particularly and Mercedes has released a small aluminum machined sound dampener that is installed inside the rubber hose to the charcoal canister. It dampens the light clicking/tapping sound from the RR of the vehicle. Give it a shot, the part is really cheap.

Holmes5518

Part Name/Part Number
1 Restrictor A203 476 03 32
1 Clamp A005 997 19 90

Holmes5518

This is where to add the dampener to

Glyn M Ruck

That is extremely interesting. All SA built W203's had those, Well certainly my old 2003 C240 had one. SA cars also had a rubber pad under the bracket that bolts the purge valve to the shock tower.

So it's the restrictor that damps the purge line. Makes a lot of sense.

In that case unplugging the purge valve would confirm it's the purge circuit that's transmitting the noise.

I would definitely fit one.

Glyn M Ruck

Holmes5518

It's not really a well known fix, even at the dealership level. The amount of affected cars seems very small so the info isn't well known among techs or service writers. His symptom sounds exactly like this issue.

Glyn M Ruck

Indeed they do! Thanks for the info!

BTW ~ (listed in the EPC as 35 A 203 476 03 32 VALVE REGENERATION LINE 001) no picture.

Holmes5518

this is what it looks like

C230 Sport Coup

To answer the original question, yes, Glyn is smarter.