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Engine Cooling Fan Stays on

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by crustyoldgrizz, May 19, 2012.

  1. crustyoldgrizz

    crustyoldgrizz New Member

    Have a 2006 Chev. Sub. when I shut the engine off and the truck is sitting for a couple of hours the engine cooling fans come on they run until my battery is dead. No engine light on. will shut off when I turn key then back on when I turn key on. Dealer up here doesn't know how to fix. changed relay no help. No messages when they plug in there happy box......lol they checked wires, put new computer in air cooling?? system, really need some help. Thanks
  2. kw70chevy

    kw70chevy Member

    why dont you wire in a toogle switch to the hot wire and turn on when you crank it up.
  3. bazar01

    bazar01 Member 2 Years 100 Posts

    This will be my last resort if I cannot find the fix.

    ---------- Post added at 08:12 AM ---------- Previous post was at 08:09 AM ----------

    On my 2001, I have a belt driven radiator fan.

    Do you have electric cooling fan on 2006 burb? If you do, try to find a electrical schematics for engine cooling and we'll try to troubleshoot.
    The fan low and high speeds are controlled by the PCM thru the low and high speed relay coils that are constantly fed with 12V + and through the PCM ground.
    My guess is either you have bad relay contacts or the PCM is providing ground path even with the engine off.

    Oh I noticed, the dealer replaced the relays and PCM. Are the fans still running on low or high speed? At least we can isolate which relay is acting up.
    Last edited: May 22, 2012
  4. crustyoldgrizz

    crustyoldgrizz New Member

    Thank you for your reply. I have no mechanical experience. I know it is the low speed fan that is running. If I pull out the Cool/Fan 3 Relay then the fan stops. This is where I am at right now. Thanks Marvin
  5. bazar01

    bazar01 Member 2 Years 100 Posts

    So there are three relays involved? I thought there are only two speeds? Low and fast fan speed.

    Time to search for a schematic.
  6. The Heater

    The Heater Member 2 Years 100 Posts

    Wow. I did not know electric cooling fans had ANY speed other than one. Very interesting. I wonder if my '94 has more than one speed.
  7. crustyoldgrizz

    crustyoldgrizz New Member

    I'm trying to send the schematic in two parts....hope it comes thru



    Capture-33.jpg Capture-34.jpg
  8. bazar01

    bazar01 Member 2 Years 100 Posts

    This site is great !

    Now I see why there are 3 relays.
    The two on the left are for the high speed operation.
    The one on the far right is for the low speed.
    The low speed relay is triggered by the PCM, then the 12V+ is passed thru the low speed relay normally open contact which closes when energized, to the first fan motor and then to the second fast speed relay normally closed contact, then to the second fan motor then to ground. Low speed operation is due to 12V power being passed on to the two cooling fan motors in series.
    When you turn off the engine, and the fans operate on low speed, pull out the third relay and see if the fans stop.
  9. crustyoldgrizz

    crustyoldgrizz New Member

    I shut the engine off the fans are running I pulled the far right (Fan relay 1) the fans stopped running. I then plugged the relay back in and they started back up again. If I leave them on they keep running until battery dead.
  10. bazar01

    bazar01 Member 2 Years 100 Posts

    Do you know which relay the dealer replaced? Did they replace all 3 relays?

    The first and the third relays are the same. They both have only one normally open contacts. Try to swap those two relays and see what happens. From the diagram, when you swap those two relays, if the low speed third relay has welded closed contacts, one fan should run in high. Let us know what happens.

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