202 repeating "sound" from trunk area? sounds elect
 

new to me 202 started today making a repeating "sound" from the trunk (right side) area.

this sound repeats approx every minute or two, as "sounds" like an electrical circuit trying to "fire" some system.

it is a soft "buzz" of about 2 seconds duration. it is best heard from the right side in the trunk, not from outside or underneath the car. it also is fairly aubible from the drivers seat.

i thought at first it was possibly the locking mechanism for the fuel door, or possibly the power antenea which was just replaced.
but my limited inspection did not seem to point to those items.

the car ran fine while this malady continued, so i do not have a clue. i thought possibly about fuel pump, but the car seems to run fine. it got dark before i could investigate further.

any info or insights would be GREATLY appreciated.

otherwise, i can only hope MB-Doc is open on Monday!

thanks, - benton in atlanata.

On my 84, a passenger managed to get the sunroof switch jammed in the "close" position. It would let out a squack about every 3 or 4 minutes until I found the source of the problem.

I have the same sound on my 94 C280. I was told that it was the vacuum pump and that it was normal :rolleyes:

Regards,

Don

it IS the vacuum pump which is used for the central locking, airconditioning system (operation of valves in the heater housing) and possible multi contour seats...
A humming sound every 2 minutes is too often and not that normal...but as long as the sound only continous for 2 seconds, I wouldn't pay too much attention to it.

greetingz,

yes, i'm sure it is vac system, but why?
 

thanks for the replies.

yes, i agree that it is vacumn related. i tested last night by turning key on, but not starting car. sure enough, what i assume is the vac pump fires every minute or so for about 2 seconds. it is a faint "bbbuuuuuuzzzzzzzz". the door locks still function.

it would make sense to me that it pulls a vac, loses vac pressure, and fires again repeatedly trying to maintain a vacumn pressure.

i think it has to be a vac sys "leak". this is my 3rd MBwith vac , and i have never seen (read heard) this before. it's not awful or terribly loud, but i want to fix the problem to maintain my sanity. it's not a problem that i could "live with".

i will investigate more today in the light of day. any insights greatly welcomed.

thanks, - benton in atlanta

PS- to MBdoc: are you open monday? have open slots?

rear buzzing sound
 

Yep! Its your vacuum acting up due to some leak(s) in the system or leaks starting to occur. I made this point several times and got no real answers, so I sent my car in for a thorough check getting all the liners in the boot out, the rear deck and rear seat, the side floor panels and the whole dash. My tech found the real culprit was not the vacuum unit(cost A$1200 to replace....and easy solution, not the right one) ,but leaks in 2 seperate items. They were rubber diaphrams in some type of plastic holders found somewhere under the dash. They had torn due to frequent movement and hardening due to age and heat. The system now only makes a first buzz on turning the key and no more for the rest of the journey. Before the repair, it used to buzz for at least 10 minutes into the journey at about 1 sec quiet and 2 seconds buzz. Very annoying and definitely NOT NORMAL. Besides this, my rearheadrest refused to drop. Now its dropping without any fuss.

repeating vac pump on 202? fused?
 

thanks to all for info.

i drove the 202 about 300 miles today. the vac pump repeat has increased in frequency, but not in duration. it fires approx every 15 seconds for about 2 seconds.

i checked the only thing that i had recently changed: the rear headrest which i had released to return to down position. i raised and released both sides several times to no avail.

the ventilation system seems to work correctly with the airflow changing to reflect the different flow distribution settings.

i also operated the central locking system several times from both the dash switch and with the key from outside.

does anyone know if it is possible to remove a fuse for the vac pump to defeat the system and still be able to operate the car?
i do understand that the ventilation sysem flaps would be affected.

any other ideas or info would be greatly appreciated. - benton

rear buzzing sound
 

Can you still drop your rearheadrest successfully when it is up by pressing the button on your dash? Please remember that this feature works only when the engine is running and there is a vacuum pump operating. The door locks operate whether the engine is running or not. Correct me if I am wrong. Total cost for this fix is a bit high for the labour required for dismantling all the parts and the dash to find the "leak". If you already know where the leak is, you would certainly reduce the time required to find it. The initial search is to start from scratch i.e. could be anywhere in the whole system of vacuum lines around the car. However, it pays to start first from the vacuum units, then those diaphrams or whtever you call those things, then look at the hoses around the car. When you say "to no avail" I would assume that you could not move the rearheadrest down at all?

vac pump requires running engine?
 

hocky, my headrest WILL still retract as normal.

i get a "buzz" without the engine running. with the key turned as far a possible without starting the engine, the repeating buzz starts and continues. now i wonder.

thanks, - benton

buzzing sound
 

How long does the buzzing last after you turn the key? Does it go on forever? Does it continue buzzing when the engine is running and you are driving the car? For how long? Mine went on for approx. 10 minutes after starting off on any journey hot or cold and anytime of day. Thats why it was so annoying with rear passengers asking me , hey what is that funny sound coming from the back. Jokingly I told them that I have some "pet" bees in my boot and they are telling me to drive carefully and not to back into another car or lamppost. LOL.

Re: vac pump requires running engine?
 

Headrest vacuum comes from the engine related vacuum system (which is WHY it only functions when the engine is ON)...not from the "central locking" vacuum pump (at least in the (older) W202s).

The vacuum pump in your car has several vacuum connection points...you probably have a leak in the climate control related part of the system (underdash vacuum valves)...NOT in the central locking (of which the vacuum only gets activated when (un)locking the car).

greetingz,