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  1. #1

    Default Radiator Fan running overtime

    Howdy everyone,
    I have often noticed a fan noise coming from my '05 engine bay even with the car turned off and have been told and read that this noise isn't a problem to concern myself with.

    About the past 3-4 trips though, this noise has persisted the whole duration of the trip. Every red light, I slow down to a stop and I hear the fan noise.

    I opened the hood and it is definitely be coming from the radiator fan, moving a lot of air, making a lot of noise.

    There is no noticeable problem with the car's performance, but the deviation from the status quo has me concerned.

    Any ideas of what this change might indicate?

    Thanks and Cheers from Indianapolis


  2. #2
    Join Date
    Feb 2010
    Virginia Beach


    Let's distinguish "fan" noises into two separate categories:
    1. climate control blower
    2. radiator cooling fan

    So, #1 is on whenever the car is running. You can barely hear it, it's quiet. It comes on precisely 50 minutes after the car is shut down to clear the AC evaporator. It runs for a few minutes, which is why, on occasion, you'll hear it.

    #2 comes on when the engine temperature exceeds a certain value (no idea what that is) and it comes on when the AC is engaged (which is nearly all the time, as defrost uses the AC to dry the air) so that the AC condenser has air flowing over it. Further, it can remain on after the car is shut down, if the engine temperature is too high (again, no idea what that value is).

    As long as #2 stops running a few minutes after shutdown, you're OK.

    However, a common failure mode for the fan module (which is integral to the fan, and not separately replaceable) is to get stuck in the "ON" position and it will run until your battery dies. In which case, you'll need a new fan, and maybe a new battery.

    Two notes:
    1. Your temperature gauge is really an idiot light in disguise. It points to the 12 o'clock position as long as the engine temperature is roughly 180-230 degrees. So the engine temperature can vary considerably, but your gauge shows the same value. You really have no idea if the engine is running a bit warmer than usual on a really hot day. That's intentional and reduces service complaints on the car. All manufacturers do it, and a scan gauge that reads actual engine temperature will reveal this to be the case.

    2. If you run the battery flat one day, please charge it all the way up using a good battery charger. A jump start is an emergency procedure, useful for getting you back on the road, but it doesn't help your battery. Getting a dead battery back to a reasonable state of charge takes several hours of running the engine. Better to do that with an electronic charger that will bring it all the way back and taper the charge at the end.
    Current Fleet:
    2016 Tundra Crewmax 4WD 1794
    2005 MB S600 (100K, Michelin AS3+, M1 0W40)
    2002 V70-XC (258K, Castrol Edge 0W40)
    2002 V70-T5 (208K, IPD bars, Bilsteins)
    2001 V70-T5 (92K)
    1932 Packard Sedan (straight 8, dual sidemounts, original paint and interior, Shell Rotella 15W40)

  3. #3
    Join Date
    Nov 2011
    Dover, NH


    If the radiator fan is on constantly it could be that the refrigerant in the AC system is low. The AC pressure switch could also be faulty.
    2005 XC70 Ruby Red
    2007 V70R GT 477/Nordkap

  4. #4


    Thanks for all the info Astro, I think youropeen has nailed it though.
    VIDA fault trace reports A/C Pressure Sensor Missing/Faulty. So either a short in the wiring, or I've lost the sensor.
    Didn't know that a side effect could be the radiator fan running full blast constantly while engine is running. I'm currently not using A/C or defrost really.
    I replaced my CCM with an ebay bought junkyard one over the winter in order to improve my max heat output, and to get back a functional blower control knob. The old one lost blower intensity knob functionality sometime last year.
    I'm wondering if the new CCM could be having a miscommunication. It's the right model number, but that is a wild card in my mind. I guess I'll start with the sensor, and hope the wiring is still ok.

    It does turn off when the engine is turned off, so I don't have to worry about the battery draining in my particular situation. The temperature is rising quickly here in Indy right now, so I need to get this figured out soon.
    Thanks for the advice.

  5. #5
    Join Date
    Aug 2017
    Pleasanton CA USA


    Danny, your situation pings my curiosity...did you receive any DIM console message?

    Does anybody know this: Is every VIDA-scannable error accompanied by a DIM warning message? Are there "silent" ones that can only be scanned?

  6. #6


    My "Check Engine" has come on and off approximately 3 times over the past two weeks. It had in the past occasionally done so in relation to a Inlet Camshaft Sensor - Faulty message (at least this is what I believe to be true based on VIDA readout)

    My "Check Engine" is not currently on, and yet the fan is still whirring away full blast. I do think the recent barrage of "Check Engine" is related to the A/C system.

    No info has recently displayed on the left side panel - the one which also will show avg. MPG, Miles to Empty Tank etc.

  7. #7


    My local Indy Mechanic suggests replacing the A/C Pressure Sensor. He also reported that the High Side Port was leaking. For $560+ he'll get it all patched up, or report back on what other error is occurring. I'm hesitant to pay this amount for the repair, but also not super confident that this is a DIY project.
    If I were to DIY, I think I would
    1) Replace the A/C Pressure Sensor (though I'm curious if this is truly failed. I do have a Check Engine light regularly occurring "ECM-520B A/C Pressure Sensor - Signal missing" but I also have a reading coming in for ECM-A/C pressure in Vehicle Communication. It's a low pressure - only 95kPa or about 13 PSI, but still I was surprised to find a reading at all. Could my A/C Pressure Sensor be good?)
    2) Fix the leak - any advice on stopping a leak from High Pressure Port?
    3) Fill refrigerant according to spec weight with UV dye to check for future leaks

  8. #8
    Join Date
    Dec 2010
    Cumbria, UK. Maine USA.


    Is the core leaking on the port?, easy fix, evacuate the system, replace the core, then pump her down and refill with refrigerant, buy the equipment at HF for a lot less than your guy would charge, failing that get a port cap with a decent seal and screw it on tight, check for leaks with soap solution, bubbles means it's leaking. There are ways to replace the core without dumping the system completely using a tool designed for that purpose,
    Last edited by AKAMick; 05-09-2018 at 08:17 AM.

  9. #9


    Good idea on using soap and looking for bubbles. I'm going to try and call back to get a few more specifics from the actual tech that worked on the car. Currently, the info I have is "High Side Port Leaking" so could be cap or core I suppose. Thanks for link on affordable tool.
    With the Sensor costing $125 and the Gauges and Vacuum Pump costing anywhere from $80-155, I'm already halfway to mechanic cost and still have to do all the labor, which I think involves removing the bumper - I read that somewhere on here right? Replacing A/C Pressure Sensor requires removing bumper. I'm still very much considering the DIY version, but just questioning if I'll actually get the value. I'll certainly learn more about the AC system.

  10. #10


    I've screwed up my courage. New High Port valve core, cap, and o-ring are only like 20 bucks, so I'm replacing all of that. Found manifold gauges and vacuum pump for $50. Parts ought to arrive by late next week. I'll keep you all updated as I no doubt struggle through this one.

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