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Radiator Cooling Fans Run Constantly

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Cory151, Mar 5, 2015.

  1. Cory151

    Cory151 Member

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    I can usually find what Im looking for with a quick search as I assume someone else has assuredly had the issue before me, but I have had no luck with this issue.

    Purchased a low mileage 2005 2nd Gen( well under 80k for under $5k) salvage titled car due to front end collision off a rebuilder. The car runs great and isn't throwing any codes.

    The issue is the radiator cooling fans run as soon a the power button is pressed, even in the morning when its cold, ICE on or sleeping. Any ideas on where to start diagnoising this?
     
  2. Easy Rider 2

    Easy Rider 2 Senior Member

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    It depends on how the fans are controlled and I don't know which it is:
    1) There is a thermal relay in the cooling system somewhere that physically closes and makes the fan run when hot.
    2) There is a coolant temperature sensor that is connected to a computer board and the signal it sends does more than one thing......like enriching the mixture on cold start and turning on the fans when hot.

    I suspect the system works like #2. If that is the case, either the sensor is bad, a wire is loose (or pinched) or the computer board is bad.
    In addition to making the fans run, it might be hurting your gas mileage too.
     
  3. Cory151

    Cory151 Member

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    I believe in the Prius the only two thing that activate fans are:

    1) Thermocouple senses a high coolant heat------turn on fans
    2) A/C is activated ------turn on fans.

    Yeah and I assume its not helping gas milage or efficiency.
     
  4. valde3

    valde3 Senior Member

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    Prius has two fans are they bought running? Even if you turn AC off?

    If bought fans are operating it can only be problem with wiring, AC-control, water temp switch, or fan relay 3.
    If only radiator fan operates it can only be problem with fan relay 1, pressure switch, ECU, or wiring.

    It’s easy to continue the fault finding from here but please tell us what fans are running.
     
  5. Cory151

    Cory151 Member

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    Here's a vid from this morning. Cold engine just after ICE kicks off.

     
  6. valde3

    valde3 Senior Member

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    I can’t tell from the video if only fan on that side is running or are they bought running? Do the fan(s) stop if you turn the AC off?
     
  7. Cory151

    Cory151 Member

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    Yes both fans run with AC off
     
  8. valde3

    valde3 Senior Member

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    First pull fan no. 3 relay and make sure that fans don’t run when it’s disconnected. Then you can measure resistance between two bigger terminals of the relay. If it has continuity relay is bad and you just need new one. If not you need to find the temp switch and test if removing its connector will stop the fans. If it did then you need new temp switch.

    It’s unlikely that those will fix the fault but while doing that you may find the spot that wiring is pinched or something. And at lest you know it’s not simple fix like that.
     
  9. Britprius

    Britprius Senior Member

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    If you require it I have the circuit diagrams for the control of the fans. As an added item please check the fans are blowing into the engine compartment from the front. The fans counter rotate and must be fitted to there corresponding electric motor. These often get swapped with front end damage causing them to blow towards the front.
    The fan motors have a two speed operation "connected in series for slow, and parallel for fast".

    John (Britprius)
     
  10. Cory151

    Cory151 Member

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    Great info, yes both fans are running and blowing toward the engine.


    Ok so is relay 3 in the driver side fuse box or in the center mounted (between engine and wipers)?
     
    #10 Cory151, Mar 5, 2015
    Last edited by a moderator: Mar 8, 2015
  11. Britprius

    Britprius Senior Member

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    All 3 relays are in the fuse box under the hood where the jump point is.

    John (Britprius)
     
  12. valde3

    valde3 Senior Member

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    Driver side fuse box (for left hand drive) its marked FAN NO. 3
     
  13. Britprius

    Britprius Senior Member

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    The strong likely hood is that the wiring has been put together wrongly or has been re wired because the re builder could not get the fans to run. Removing the connector to the engine temperature sensor should turn the fans off if the sensor is at fault "which I doubt".

    John (Britprius)
     
  14. Cory151

    Cory151 Member

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    Pulled the #3 blue terminal and check the resistance between the bigger copper terminal and got infinity, so it looks like the relay is good. Also when I pull it the fans shut off,when I plug it back in the fans turn on.

    Where is the temp switch or sensor usually located? image.jpg
     
  15. exstudent

    exstudent Senior Member

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  16. Cory151

    Cory151 Member

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    Irrelevant. That guy had a 9 year old 12v battery, a falling (cell block 10) traction battery and a failed catalytic convertor. The car I am referring to throws no codes and the HV battery just received a balance charge, coolant change and transaction fluid change.
     
  17. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Get the electrical wiring diagram at techinfo.toyota.com so that you can see how the engine cooling system is supposed to work. Then maybe you can figure out where the problem is with your car, which probably is associated with improper repair of the collision damage.
     
  18. Cory151

    Cory151 Member

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    Thanks but I'm not paying for wiring diagrams if somebody can't post one I'll simply compare the wiring from one of the other Prii.
     
  19. ikefor

    ikefor Member

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    You may want to test the r134 pressure switch. There is a simple test somewhere in the forum where you can use a short wire to test the switch.

    If you pm me your email address, I can send the wiring diagram to you.

    Considering the front end collision, the absence of a code from the vehicle does not necessarily mean the absence of a fault, it only means that the car is not registering the fault codes and this is likely based on the way the car was fixed.

    I had a similar issue with a rav 4 which had a front end collision and afterwards didn't register any codes.
     
    #19 ikefor, Mar 6, 2015
    Last edited by a moderator: Mar 8, 2015
  20. exstudent

    exstudent Senior Member

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    Hmm, you both have an improperly wired fan. You missed "radiator fan had been directly connected such that it starts with the car on ready (ig on)." Yes, the poor lad from Nigeria is suffering from other issues as well. But both of you have the same underlying wiring issue.

    Looking at the wiring diagram for both fans (Condensor & Radiator), its possible the "rebuilders" bypassed the junction connector for each fan motor, which explains Ready = fans on. Diagram attached as a courtesy.

    You saved some money on buying a salvaged. Don't cheap out on $15 and the ability to get the Official Toyota Service/Repair manual. It is insanely comprehensive, and the best automotive $15 you will have spent. Link for info on Toyota Service Manual, and printing solutions contained here: Where to get Prius v Parts and Service Manuals? | PriusChat

    If you don't own mini VCI cable, get one; $25 at Amazon/eBay. This will give you the same diagnostic capability as dealers, as they use the same cable (granted a genuine cable vs knock off imitation) and software (legitimate vs a hacked copy). This being said, many here have been using the hacked stuff off Amazon/eBay w/o any problems, doing maintenance and reading codes! You can now read the codes w/ accuracy (generic readers miss a lot of codes and give false codes).

    Click this LINK, and choose any mini VCI cable; I'd get the cheapest one (new or used). You can always find a newer software version of Techstream somewhere on the Internet.

    READ ME FIRST link. The Tundra boys provide an easy ABC, 123, for mini VCI. You should have no further questions after reading this. There is even a link w/in this article for a 64bit Window's set-up.

    Hardware Requirements link, by Toyota, just note the speed and RAM requirement for your soon to be Techstream laptop.

    To be data safe, assume the hacked Techstream software has malware. This laptop should be a spare "junker," used only for Toyota diagnosis/maintenance; NO email, NO online banking, NO nothing where a user ID and password is ever entered.
    Some people have reported success using a Mac laptop in some Windows XP emulation mode.
     

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    #20 exstudent, Mar 6, 2015
    Last edited: Mar 6, 2015
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