Buzzing sound after shut off

Dave0304XC · Post by **Dave0304XC** » 04 Dec 2020, 08:26

Hello! 2003 XC70, for several years, when I shut off the car, I hear a intermittent buzzing sound coming from under the airbox. Even if I just turn the key on (like just to put the windows up) it will buzz for about 2 seconds, then quiet for about a minute, then buzz for 2 seconds... Does this for about 5 minutes or so. I heard it's the brake vacuum pump under the air box. Brakes feel fine, sound is just an annoyance. I could buy one at my local U Pull It junkyard for probably $10, maybe less, but if it's not a simple replacement, I'll just put up with the buzzing noise. Is there more to replacement than unbolting and changing it out (need to bleed the system?)

Thanks! Dave

Post by **MoVolvos** » 04 Dec 2020, 20:00

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Our C30 use to make this noise but it stopped. Our S80 has been making that noise since we purchased it almost two years ago. Will need to get to it besides a dozen other things

. At this point I've not taken the time diagnosis to see exactly what is buzzing but it's definitely the noise in the video.

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Post by **oragex** » 05 Dec 2020, 11:56

The pump is fine, but something is triggering it. Start by looking at the vacuum pump switch, at the junkyard it's quite easy to find recent ones, they have like black tape around. Also go around the vacuum hoses, one going to the engine, another to the booster. But mine (video above) was a leaking brake pedal plunger seal. You may want to look at the channel for this, and try having a look at your seal. I'd say, if it didn't come out in a corner, it may still be ok-ish for a while but risks burning the pump - which is not hard or expensive to replace with used one. For the seal, can get the ATE booster at Fcpeuro.com, replacement is not quick, see youtube how to remove the 4 securing nuts faster

Dave0304XC · Post by **Dave0304XC** » 07 Dec 2020, 14:28

Oragex- So I just went out to take a look at that little switch- the thing with the electric connector and the three large rubber lines connected. Probably original, when I touched it the plastic crumbled- broke apart! Piece of cake to get one of those at the junkyard- and little stuff like that is usually just a “have a nice day” sort of thing. I strapped it together with a couple of zip ties for now. Is the buzzing usually a problem with that switch (I can easily try a couple from the junkyard) or is the problem usually further upstream? Dave