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The AWD Warning Light was coming on from time to time & there was a "knocking" sound from the rear while making turns.

So, I took it to the dealer. They said the AWD sensor was defective & the noise was from movement in my hitch (bogus). Charged me $350 to replace the sensor & determined that, while it was defective, it was not the root of the problem.

The real problem was a defective rear differential-viscous coupler. $1300 to replace (labor & parts).

All of this is out of pocket, as I am the 2nd owner of my Santa Fe which has 70k highway commuting miles.

Very disappointed in all of this. Not likely to ever buy another Hyundai.
 

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So sounds like the rear diff bit the dust, clunking sound while turning classic symptom. Could be a mfg defect, could be it was low on fluid or subjected to physical abuse at some point.

So to me with the AWD warning light coming on - is an indication that the abs sensors might have been working correctly - if that was the sensor that was replaced. Faulty ABS sensor will light up the brake light.

I think you possibly have been hoodwinked on the $350 bill.
 

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These 4wd systems are very sensitive about all 4 tires being the same diameter.

When there's difference in tires' diameter, the system thinks the wheels are slipping and sends torque to the rear wheels.

Since they aren't slipping, the difference in speed between wheels continues and this puts the system in a bad cycle.

Even differently worn tires can cause this.

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These 4wd systems are very sensitive about all 4 tires being the same diameter.

When there's difference in tires' diameter, the system thinks the wheels are slipping and sends torque to the rear wheels.

Since they aren't slipping, the difference in speed between wheels continues and this puts the system in a bad cycle.

Even differently worn tires can cause this.

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what he^^ said. this is a HUGE caution in the subaru forums. if the tire sizes are off more than 3/32"(might be more, i forget), and the drive system has viscous couplings, which most do, then the viscous overheats and dies. whenever testing out a used car, drive the car in a full lock circle. if the viscous is dead, it will make that knocking sound, and the car will kinda 'skip'
 

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Hard to say what the root cause was. It "looks" like the Dealer might have miss diagnosed it on the first attempt, but having been down that road myself I'm not going to condemn the Dealer without knowing more. Some times there is more than one issue or issue 1 leads to a consequential failure and issue 2. It does happen....


Great point by RVB however....Even if it was not a factor here, the issue with tire size is a concern in just about all AWD and 4WD systems. No way to know on a used vehicle if a prior owner might have compromised the system by running incorrectly matched tires at some point. I can say that we do see that issue on occasion during the winter. A tire gets punctured and the lone tire replaced or perhaps two wear out due to a lack of proper rotation and the owner has only one or two tires replaced while 0/ 4WD components that can lead to a mechanical failure. I include 4WD in this as many 4WD systems on newer vehicles have an "Auto" setting and owners tend to leave the system set in Auto. For most vehicles they should be selecting the 2WD position in normal weather and switch to Auto or 4WD HI only when the roads are slippery and use of the system might be necessary. Again....Excessive and unnecessary wear or components is the main issue......
 

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what he^^ said. this is a HUGE caution in the subaru forums. if the tire sizes are off more than 3/32"(might be more, i forget), and the drive system has viscous couplings, which most do, then the viscous overheats and dies. whenever testing out a used car, drive the car in a full lock circle. if the viscous is dead, it will make that knocking sound, and the car will kinda 'skip'
Hyundai uses a wet multi clutch pack, solenoid activated with an open diff, I would think on the newer SFS a better way to test the rear diff setup would be to engage the AWD lock, then put the car in drive, then reverse, then drive it a tight circle - to see if any clunking or odd noises are heard from the rear end.

A clunk when turning is usually a sign of wear in the diffential gears themselves , whether AWD is engaged or not.
 

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Hard to say what the root cause was. It "looks" like the Dealer might have miss diagnosed it on the first attempt, but having been down that road myself I'm not going to condemn the Dealer without knowing more. Some times there is more than one issue or issue 1 leads to a consequential failure and issue 2. It does happen....


Great point by RVB however....Even if it was not a factor here, the issue with tire size is a concern in just about all AWD and 4WD systems. No way to know on a used vehicle if a prior owner might have compromised the system by running incorrectly matched tires at some point. I can say that we do see that issue on occasion during the winter. A tire gets punctured and the lone tire replaced or perhaps two wear out due to a lack of proper rotation and the owner has only one or two tires replaced while 0/ 4WD components that can lead to a mechanical failure. I include 4WD in this as many 4WD systems on newer vehicles have an "Auto" setting and owners tend to leave the system set in Auto. For most vehicles they should be selecting the 2WD position in normal weather and switch to Auto or 4WD HI only when the roads are slippery and use of the system might be necessary. Again....Excessive and unnecessary wear or components is the main issue......
Yes, that's the point. To get things worse, there's no way to disable 4wd in our Santa Fe's

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