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Thread: Can someone explain how haldex AWD works?

  1. #1
    Join Date
    Jun 2018
    Location
    Vermont
    Posts
    36

    Default Can someone explain how haldex AWD works?

    We just replaced a howling rear diff on an 04 xc70. Now after getting rid of all the network issues (here's that: http://www.volvoxc.com/forums/showth...-s-how-it-went )

    We are at a loss as to when and how haldex works. When we got the car and found the issue on jack stands, all 4 wheels turned.

    Now only the fronts spin. On dirt and pavement, in the air, only front wheels turn.

    I took my car out, and same thing 2 wheel peel. Mine has not been worked on, and they both have no messages on the dash other than SRS.

    Ugh, someone explain the ins and outs on haldex?

    How do I know if and when the AWD works???

  2. #2
    Join Date
    Dec 2009
    Location
    GA
    Posts
    1,089

    Default

    Quote Originally Posted by Hamfist View Post
    and they both have no messages on the dash other than SRS.

    How do I know if and when the AWD works???
    DEM codes will not cause a check engine light (they don't consider it emission related) or any indication on the dash


    The DEM tells the haldex clutch to engage (with hydraulic pressure generated from an electric pump that goes bad) when the front wheels spin faster than the rears. By the way when the pump goes bad sometimes it fries the DEM. There are helpful Diagnostic flow charts at Xemodex.com

    https://xemodex.com/us/knowledgebase/dem-flow-chart/

    First step would be to scan the car with a scan tool capable of talking to the DEM. (VIDA will give the most info) And go from here.
    Last edited by hoonk; 10-09-2018 at 06:14 PM. Reason: spelling

  3. #3
    Join Date
    Jun 2018
    Location
    Vermont
    Posts
    36

    Default

    Quote Originally Posted by hoonk View Post
    DEM codes will not cause a check engine light (they don't consider it emission related) or any indication on the dash


    The DEM tells the haldex clutch to engage (with hydraulic pressure generated from an electric pump that goes bad) when the front wheels spin faster than the rears. By the way when the pump goes bad sometimes it fries the DEM. There are helpful Diagnostic flow charts at Xemodex.com

    https://xemodex.com/us/knowledgebase/dem-flow-chart/

    First step would be to scan the car when a scan tool capable of talking to the DEM. (VIDA will give the most info) And go from here.

    Blargh, both might be bad!! Sigh... Gotta get my vida

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