Mystery fan noise in cabin when ignition off – Vito W639

I recently was sent a question with regard the hearing of a fan noise/running in the cabin of the Mercedes Vito W639 when everything is turned off. This noise is often mistaken as the ventilation fan (blower) running, even though the fan position switch is at the off position.

Here is the original question:

HI, I recently purchased a 2008 vito W639 111 and when I start the
engine the heater fan is also on, even thou the fan switch is in the
off position.
Have you heard of this on any other vans and is there a remedy that I
can do to fix this issue.

Here is my reply:

I can only assume that what you are hearing is:
There is a small fan (like a computer fan) that operates under the control of the ECU that cools the large plastic fuse/ECU box under the bonnet, this obviously has a mechanical connection to the area behind the dash on the passenger side. As this fan ages it becomes more a little more noisy and can sound like the cabin air fan is spinning on low RPMs. It also runs when the ignition is on and engine not running and continues for a controlled period after the engine is stopped, you can force it to stop by turning the ignition on and off a second time.  There is also a small fan that cools the rear of the radio (similar thing), this is on the inside right of the radio cage within the dash if you were to remove the radio.  This one gets really noisy with age !
So nothing to worry about unless the cabin air circulation fan is actually running!, which I think you may well be mistaken about.
Hope this helps, if not just email back with a little more detail.
fuse box fan W639

Mercedes Vito w639 Fusebox Fan

A further note –
Just as a point of note the fuse box/ECU cooling fan is at the bottom of the plastic fuse box housing in the engine bay (picture above) and once its bearings get a little worn the box aids to amplify the noisy fan motion and it appears quite loud in the cabin area, often mistaken as the cabin ventilation fan running.

29 thoughts on “Mystery fan noise in cabin when ignition off – Vito W639

  1. I have a 2009 model and wondered this for a while.
    There is a likely a similar small fan in the dash in your model as well, behind the right hand side of the radio. I assume it is to keep air circulating around the radio and this are, as there is heat radiated out of the plastic heater vent behind and from the radio. It stays on for about 15 mins after the ignition is switched off.

    1. Indeed correct, as outlined in the text the radio fan lies on the inside right of the centre dash aperture. This fan is basically a computer type brushless fan, almost like a processor fan. It is mounted on a crude steel L bracket and easily removed/cleaned. I suspect its a standard small form factor 12v PC fan if you ever needed to replace it.
      All the best Steve

  2. My 2007 Vito has same fan noise coming from left front passenger dashboard area. definitely not from the radio nor cabin air fan so must be ECU related. Thanks Steve for confirmation.

  3. What a relief, it been driving my missus mad for ages. I have been able to show her this and has solved another constant question whenever we go anywhere in it.

    1. Hi Lee,
      This fan does shut off after a short time, probably when the temperature in the fuse box falls below a predetermined level. It is also a very small fan and does not draw a great deal of current. Its more likely you have an interior light issue, even if there is no dome light on (passenger or cargo area) there is a chance the wiring (usually in the rear gets damaged).

      It could also be a faulty alternator – back feeding through the regulator diode pack within the alternator, taking the alternator out of circuit will prove this. You can measure current between the positive battery post and the lead with a test meter and compare before and after readings. Remove circuit fuses one by one and see if you can isolate the drain to a particular circuit, this may help pin pointing the problem.

      Remember it could just be the battery is past its best, and the immobiliser kills it overnight. Have it drop tested from fully charged by some one with the proper battery load tester (most auto electrical outlets).
      Hope this helps

      1. Hi.
        I have the same problem with my vito. The blower or fan stays on when the car is off and it drains my battery. Mercedes said it could be a relay. Still trying to find relay.

      2. Hi there Raelene,
        As I understand the small ECU cooling fan is driven directly from an output signal from the ECU, I doubt there is a relay for this specific cooling fan. I would stab a guess that the ECU is staying ‘live’ and not turning off as it should. This could be attributed to a power distribution faulty or as the dealer said a sticking relay. The constant powering of the ECU would also be more likely to drain the battery over-night than the operation of what is in essence a very small DC fan drawing a miniscule amount of current – my observation here would be to investigate reasons why the ECU may not be powering down fully – The ignition switch controlled power circuits would be my first start.
        Good luck and please let me know what you find.

        All the best

  4. Hi there. I have a 2005 Vito and the electronic box fan warning light has just illuminated on the dash board. Is there a fuse that controls the fan?

    1. Hi Gary,
      The fan is located in the electrical box under the bonnet (The big box on the right looking in, that houses the fuse board and other components) The fan is probably faulty, bearings in these have been known to give problems. Sometimes a good clean of the mechanical parts of the fan and the wiring connections are enough to get things going again – but worst case a new/replacement motor and probably safer to fit new as its it an unpleasant job to get to. The worst part is removing all the electrical equipment and wiring from the fuse/control box to gain access (Its right at the bottom!)

      Best Regards Steve

      1. Steve

        Thanks for your reply. I had a look for the fan inside the large fuse box and couldn’t see it.

        So your saying its underneath the fuse panels and I’ve got to take those out to get to it?



  5. I have a 2008 vito 109 cli.on acceleration there a funny blow ing noise coming from passanger foot well .on de acceleration it stops till you accelerate again ?

    1. Hi James,
      This sounds like you have a split turbo charge hose or badly sealed joint. The noise is most probably turbo boost pressure escaping under load. If you look to the passenger side of the engine you will see hoses from the intercooler to the inlet manifold, check these. Usually there will be black oil spray indicating the area of the leak.
      All the best

  6. My vito 2006 won’t start. Roadside assist came and jump started it. Told me if it happens again just to call him..not the best solution. So I can say this. The battery is getting drained by an unknown source. Please help. I have read you can add a switch to cut off the battery when you take the key out..this sounds like a work around. Is anyone aware what may be draining the battery when the car is switched off?
    Could it be to do with temperature? The reason I ask is the only thing that changed was I turned the internal temp gauge up just prior to the problem occuring..
    Any help would be appreciated.

    1. Hi there Lynette,
      It could as you say be any number of things but I would be looking to a fault in the alternator rectifier pack. It is possible and often the case that a single diode in the pack goes faulty discharging the battery. I would take your Vito to an auto electrician and have the alternator tested as a first step then if that proves to be OK move forward with other diagnostics. with a bit of luck a new alternator may get you back running again.
      All the best

  7. Hi Steve
    My 2008 Vito smells of diesel fumes not only when it is running but the smell is there when it is switched off until start-up the following day. I have placed a curved chrome extension(facing towards the ground) at the end of the exhaust pipe hoping this would fix the problem thinking the rear door rubber was worn letting in the fumes but the smell is still prevelent. Could it be leaking in from some other area that you may know of?
    Any help would be appeciated, regards.

    1. Hi Grayham,
      It might be worth looking under the air filter box, remove this and see if you can see anything around the rocker encasement (black plastic cover over the injectors) that would indicate an injector was leaking. Have a look here this should give you some pointers of what to look for, you may even see/smell diesel misting. To be sure you would have to take this cover off to inspect the injectors. The reason its strong smell could be in the cabin is that the intake/pollen filter is in very close proximity to the engine behind the removable panel in the centre of the windscreen plastic lower panel just above where the injectors sit.
      I hope this is at least a small help to finding the source of the problem.
      All the best

  8. Is there a way to temporarily disable this fan without overheating the Ecu? I need to do some audio calibration on my car stereo, but the microphone picks up the fan noise. This would be standing still with engine off, in a vito w639.

    1. Hi Joseph,
      No way I can think of except to temporarily disconnect it. If you are however testing with ignition off (no engine running) then operating the key twice with engine off will often cause it to stop running ahead of its time out period.
      All the best

      1. It does turn off eventually, but only when the ignition is off. Problem is, I can’t tune the audio system without the ignition on. I can’t find a fuse for the fan, and can’t see the plug either. I’m not in the mood to take the fusebox apart either.

        I guess my only option is to bring in two extra batteries and run the stereo and mic off that while doing the tuning. What should have been a 10 minute job is now a days work.

        Thanks for the info Steve.

  9. I’ve got 3 problems I can’t understand on my 2010 Vito Dualiner.
    1. I have the same fan noise in the passenger footwell and a quieter one above the radio which seems to stop if I turn ignition on and off a second time.
    2. The radio works fine but and if I put a cd in the player it plays ok but then the trouble starts. If I want to eject it and put another cd in it wont accept another cd. Pushing harder makes no difference. I then try to turn the radio off and on and the radio wont turn off. If I switch the engine off it stays on. If I switch the engine back on it turns off. If I then switch ignition off again radio stays off but you can hear a whirring sound as if the cd is trying to load. The only way to stop it is to put a cd approx. an inch inside the slot then withdraw it and the noise stops. What could this be?
    3. Last but not least an irritating one. My warning light illuminates telling me I have a problem with my lights but when we check they all work perfectly. Warning light doesn’t always illuminate sometimes I can put the lights on and no warning light at all? Would value your comments folks. This is the first Merc I’ve owned.

    1. Chris, there is a cooling fan under the fuse box casing under the bonnet that vents into the passenger compartment, that fan is going to be the source of the noise in the footwell. There is also a cooling fan at the rear of the Audio10 radio CD player and that too gets more noisy with age.
      There is a problem with the CD loading mechanism on your CD player by the sounds of it. You can get a complete Audi10 CD unit off Ebay and strip it to swap over the mechanism, quite straight forward, as I remember one ribbon connector and two screws once you get the lid off. Doing this totally avoids the CODE issue of the player as you are only swapping the mechanism!
      Good luck

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