Found this on another site, posted in 2021:
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The AWD coupler fail explained: my conclusion
Based on all reports on this forum about this issue, and adding the revealing results of my own technical investigation on the operation of the coupler published last summer, (by reading the coupler pressure on the run in real time ) the logical sequence of coupler failure can be considered a totally expected mechanism. What follows confirms and unites all the elements that were reported in the abundance of threads about this issue.
OPERATION:
Contrary to the "reactive" logic of many AWD systems (that react by applying AWD to the rear wheels when front wheel spin is detected) the KIA/HYUNDAI system works by anticipation...that is full time, and proportionally to throttle in the following manner:
-hydraulic coupler pressure is applied by a hydraulic pump: the pressure goal is set by the AWD computer and read by a pressure sensor.
THE pressure "goal" is proportional to throttle position.. the more you push, the more pressure is applied to coupler; however this goal is lowered as the car speed increases in such a way that at highway speed, no significant pressure is applied even at full throttle. IN addition, the LOCK switch INCREASES the ratio of command, adding an extra 50% pressure at standstill ; this additional ratio falls progressively down to zero at around 25 mph/40km/h. LOCK is NOT a full lock.(see note 2)
FAILURE MODE
Recent data by other forum members about the "learning" number and the way screeching the rear wheels is seen to INCREASE with mileage suggests that the learning "number" increases the ratio, probably too much, with mileage; now if you throttle hard at low speed (where the pressure/throttle ratio is maximum) starting in a tight curve, the coupler will drive the rear wheels harder: then one of many things will happen: rear wheels will slip on sand , or will screech on the asphalt, or if tires have a good grip, will slip the coupler clutch....or will even destroy it (as described in several threads). see note 1
From the start, based on reports from others on this forum, I felt that there was a real problem with this AWD system that I qualified as caused by poor botched AWD firmware. In consequence, I have installed an AWD disable switch (like exists on a lot of AWD cars, including wife's Suzuki SX4) , letting me manage AWD at my own will. OF course, I think the 2.4 "4 banger" does not stress the coupler as much as the 3.3 V6 but I like to play safe . Turning off the AWD system also possibly inhibits the "learning" mechanism that, from all reports that I have read, is also a probable factor in this issue.
Conclusion:: as delivered, the Dynamax AWD system (called HTRAC at Hyundai) is destined to fail. Mild use of throttle in curves at low speed will retard failure. Turning it OFF (by removing AWD fuse or installing a switch) when not required can save it.
note 1: in turns, the rear wheels describe an arc that stays inside the front wheel arc...so rear wheels turn slower than front wheels. Since these AWD cars have NO center differential, something else has to give.
note 2: a corollary of this is the following: on upslope... if front wheels are on a very slippery surface and rear wheels on solid, it might happen that one uses little throttle pressure to avoid spinning the front wheels....and consequently, there will be only a low pressure on the coupler, not enough to drive the rear wheels hard: instead the coupler will slip, so the car will be stuck there with no traction at all. This has happened to me and others have reported the same on this forum.
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