GMC Truck issue

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  • mforsta

    Pops
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    4   0   0
    Jun 25, 2012
    494
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    Denham Springs
    Folks I need a little info on my truck. The specs are 2012 GMC Sierra 5.3L. The engine cooling fans have been coming on high speed at start up when the engine is cold. The fans will high speed fan come on and off while driving also. This started about 2 months ago. Anyone have this issue before and have a solution, please pass it along.
     

    Specularius

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    Oct 5, 2008
    599
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    N31 20, W92 14
    Could be a faulty fan relay. Probably an ice cube type relay. is the check engine light on and have you checked for any diagnostic codes? AutoZone will check for codes for you if you don't have a code reader.
     

    DWT

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    Jun 9, 2008
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    New Orleans
    Disconnect the battery, wait a minute, then reconnect. If the problem remains, it's time for a trip to the repair shop.
     

    Robbie

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    Nov 8, 2011
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    Elmwood, LA 70123
    Google it, GMC fans have a website I'm sure.
    But sounds like cooling fan temp sensor may be faulty.
    youtube will also have vids and such, that's how I fix mostly all our cars.
     

    LS1RX7

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    Aug 27, 2010
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    Slidell
    I would guess that is normal if the AC is on. The same fans cool the condenser that cool the radiator. The condenser gets hot regardless of engine temp. See if it does it with the AC off. Also it started (you noticed) in the middle of summer coincidentally.
     
    Last edited:

    BigP623

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    Aug 27, 2014
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    Lacombe, LA
    I have an 08 and it does the same thing during the summer. Shes not overheating and temps in normal range when driving/idling so I just let her be. They are loud as hell tho lol.
     

    jdindadell

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    Feb 14, 2010
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    A/C fan must be triggered to allow the A/C compressor to be triggered. A/C pressure will go up very high and fast if the condenser is not seeing airflow. I have noticed that the fans on these trucks are loud.

    Turn the ac off before starting the truck and see if the fans come on. If so the fan temp sensor may be bad, but usually that is built in to the cooling system temp, so if the truck temp gauge is working correctly it may be something else.

    These are multi speed fans, so the fan controller may have crapped its pants, and it is defaulting to wide open.
     

    RaleighReloader

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    Jan 30, 2015
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    Baton Rouge, LA
    The air conditioning in a motor vehicle relies on airflow. The temperature of the engine doesn't matter; when the air conditioning is on, it's pretty normal for the secondary fans to kick on.

    If you turn your air conditioning off, do the fans still come on when the engine is cold?

    I just checked on my 2017 GMC, and it does exactly the same thing. If that's the case (and if the engine temperature is staying in the correct range), then there's probably nothing to worry about.

    Mike
     

    paddle007

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    Apr 15, 2009
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    Covington
    Lets try to get the big picture here.
    How long have you owned/driven this truck?
    Is the current fan cycling event different now?
    How long does it for the fans to come after a cold start?
    Is the AC or defroster on when it is started cold and the fan cycle as you describe?
     

    mforsta

    Pops
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    Jun 25, 2012
    494
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    Denham Springs
    Sorry for not responding, been on the road for a couple days now.

    I am the original owner and the truck has 108,000+ miles on it. The fan comes on high speed on cold starts but only when the compressor is needed, ie, on cool morning the compressor is not needed so the fan doesn't come on. On cold starts with compressor on the fan comes on one high speed right of the bat.
    I haven't had a chance to do a whole lot of diagnostics of yet but will tear into next when I get back in town.
     

    buttanic

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    Dec 2, 2010
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    LaPlace, LA
    I have an 07 Suburban, on a cold start with the AC off the fan will not start until engine temperature comes up. If the AC is on the fan will start on low when the engine is started and as the engine heats up the fan will switch to high speed with the AC on. It will switch between low and high as needed. Moving down the road high speed is not needed because of air flow. If you are sitting in traffic the fan will switch to high.
     
    Last edited:

    paddle007

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    Any updated info with your truck? Inquiring minds want to know.
     

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