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Discussion Starter · #1 ·
Greetings all, I have a 2004 2.5T and just recently noticed a sort of whining or whizzing noise coming from the front drivers side of the car. I know it's something electrical as the noise is present whether the engine is on or off, but only as long as at least the ignition is on. It's not one of the many cooling fans of the car (cooling, A/C or ECM/TCM). It actually sounds similar (though louder) than a fuel pump sound. An '01 S40 I used to have had a noisy fuel component by the tank, and it's comparable to that. With the hood open, the sound appears to be coming from the intake airbox area. I'm not overly concerned, just curious what that is or might be. No CEL, red/orange triangle or any codes being given off, no reduced power either. Just a whining sound that's sometimes annoying.
 

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Do you have HID's? With ignition on/engine off, turn the headlamps off and run just the corner lamps and see if the noise goes away. Could be a ballast, i've had them whine before, and have since removed them completely to draw less attention when i'm busy going 100mph.
 

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Discussion Starter · #3 ·
lol!! Actually I'm going to be trying out LED low beam bulbs soon here. I DO have HIDs however. The buzzing happens still with only the parking lights on (knob in the middle position). I can actually hear the sound faintly while in the car with the engine on, so it's pretty audible. Is there anything within the intake that could make noise? MAF?? But I don't think it would be active without the engine running... I'll take a better listen at the ballasts themselves. Thanks for that tip! :cool:
 

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Discussion Starter · #5 ·
I can check that out! I know that with the engine running, if I rev it, the noise lowers in pitch for a moment as the engine revs back down after releasing the throttle and then returns back to the same tone pitch it was at. The sound is reminiscent of hearing a vacuum cleaner in a room next to you.
 

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Discussion Starter · #6 · (Edited)
Bingo!! Antherzoll hit it on the head!! Stopped by a local Volvo only specialty shop and had the owner take a listen. Turns out it's a possibly a bad brake vacuum pump sensor. He unplugged it for the time being and explained that the sensor makes the vacuum pump run when the car is cold, then it should shut off once warm as it's there to warm everything up initially. He said if the sensor goes bad, it could blow a fuse and cause the whole vacuum pump to seize and fail, which would also cause the steering to become stiff. Thing is, I'd hear the pump buzzing away loudly, even with the car warm, and even after long drives as of recently. This wasn't something I ever noticed until about 2 weeks ago, so I knew it wasn't normal. He told me better to replace a simple sensor, than risk needing a $300+ part in possibly not much time. And well know that's usually at the least convenient time possible. He also explained that with the sensor unplugged for now, braking will be stiff when the car is cold until it warms up. I can live with that until I have the new part.
 

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WTF!!! Volvo specialist unplugged the vacuum assist pump and let you drive off.

A cold engine does create less vacuum than a warm engine, but when the engine is off or on load/in boost the vacuum assist pump will maintain brake circuit vacuum. In the event of emergency stoping or complete engine failure it's possible that you'd be left without vacuum assisted brakes. The sensor is dead easy to install, it's right infront of the air box, but it could also be a brake circuit vacuum leak. I suggest that you plug the sensor back in and allow it to operate even though the switch is faulty until you can get a replacement. Think about it, would you risk your safetly/vehicle to save a pump???

I don't understand how any of this system will affect steering in the event of complete vacuum pump failure, two complete different systems.
 

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Discussion Starter · #8 ·
I can't figure that out either, the correlation of the brake system to the steering system, didn't make a whole lot of sense. But yeah, he unplugged it and said I should be OK until it's replaced... I'll plug it back in for safety though. I'd much rather be safe than sorry. On that note, felt NO difference in the brakes this morning with the car cold. In searching, is this the part I'm looking for?
 

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Discussion Starter · #10 ·
Yes, that's it. About a $70 part I was told, assuming that's stealership cost. ;)
 

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The pressure sensor usually fails and causes the pump to run constantly. Replace the switch and it should be fixed. On cars with speed sensitive steering, some models share the circuit with the brake assist pump. When the switch goes bad and causes the pump to run constantly, it eventually kills the pump and blows the fuse at the same time, thus cause the power steering assist at idle to become stiff. I have seen this on older XC90's
 

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Discussion Starter · #12 ·
Mysteriously I don't hear the pump running constantly anymore. But with no codes and everything functioning, I'm assuming nothing blew, pump or fuse wise? The switch has been plugged back in since the day after it was diagnosed...
 

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Discussion Starter · #14 ·
Yes it was. Actually it ran when the key was to POS II, and with OR without brake pedal input. Just ran off the bat with the ignition on. Since disconnecting it and reconnecting the following day, I haven't heard it run since.
 

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If it acts up again, replace that switch. The only other reason it would run after ignition is off is if you had a small leak in the booster or lines holding vacuum in the system, once it sees a drop of vacuum below a certain threshold, it will kick the auxiliary vacuum pump on until its happy again
 

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Discussion Starter · #16 ·
Sounds good! Debating if I should have a new switch waiting just in case...
 

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From my experience, if you have a part number dealers are usually pretty quick to get parts in but comes at a price. Online supplies will be cheaper per part, but it will take more time and shipping cost (some have free shipping, but there is usually a minimum you have to order).
 

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Discussion Starter · #18 ·
That's true! FCPEuro has a good price on it. For some parts though, when you add on shipping costs it'll come near even with dealership cost for the part.
 
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