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Discussion Starter #1
So, new little "glitch" I discovered today.

Took a drive in the mountains. As I descended, my battery charge reached 100% about halfway down. About 3/4 of the way down, battery having been at 100% for some time & continuing in "charge" mode, the engine kicked on, and at near full throttle. Stayed that way until I tapped the accelerator, at which point it revved down to idle. Happened a total of 3 times during the descent. No OBD code thrown, no other symptoms.

Anyone else ever experience this?
 

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Sounds like engine braking; I would guess it was in a low gear/high rpm (thus loud) but with zero throttle, not "near full throttle". When you tapped the accelerator, it figured there is no need for braking any more, and shifted up.
 

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100% on your display doesn't mean 100% in your battery. More like 80%. So the car allowed regen to continue for a while, and then decided that to continue regen would damage your battery. There is nowhere to dump the energy produced by regen if the battery cannot or will not accept additional charge. I gather you were on cruise control to maintain your downhill speed? Doesn't really matter but the same thing would have happened had you been depressing your brake pedal instead. But because you were on CC, the demand for constant speed initiated engine braking. This did not use any fuel.

PHEVs with a larger battery have an advantage in this scenario in being able to recapture more energy. But the constraints Kia engineers put on overcharging the battery will end recapture there too. The BEV shouldn't have these problems unless you live on top of a large hill and fill to capacity before setting out. Such owners should never charge to 100% at home. Otherwise, going up a hill runs down the battery, and going down recharges it, never more than it has already discharged. The HEV using ICE to climb hills (and charging at the same time) will experience what you did.
 

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100% on your display doesn't mean 100% in your battery. More like 80%. So the car allowed regen to continue for a while, and then decided that to continue regen would damage your battery. There is nowhere to dump the energy produced by regen if the battery cannot or will not accept additional charge. I gather you were on cruise control to maintain your downhill speed? Doesn't really matter but the same thing would have happened had you been depressing your brake pedal instead. But because you were on CC, the demand for constant speed initiated engine braking. This did not use any fuel.

PHEVs with a larger battery have an advantage in this scenario in being able to recapture more energy. But the constraints Kia engineers put on overcharging the battery will end recapture there too. The BEV shouldn't have these problems unless you live on top of a large hill and fill to capacity before setting out. Such owners should never charge to 100% at home. Otherwise, going up a hill runs down the battery, and going down recharges it, never more than it has already discharged. The HEV using ICE to climb hills (and charging at the same time) will experience what you did.
I would go along with this explanation. Happened to my Fusion Hybrid once and it sounds like the ICE was going to blow.
 

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Discussion Starter #5
Thanks to all for the replies & explanations!

And to clarify, no cruise control active during the drive. The mountains here can be steep, but this particular drive is low speed (avg 30-35 mpg) and a lot of coasting without having to brake much at all, so no need for cruise. Plus I have the LX with the rather poor cruise control system so I really only use it on long stretches of flat highway.

And yes, it DID sound like the engine was about to blow, or would have if left unchecked.
 

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I had about the same thing happen in my LX, when I was on a loooong descent out of the mountains. Not real steep, just long and constantly descending. The battery display went to 100%, then shortly after the engine came on. I was not using CC, just coasting with brake use as needed. That was the only time I've experienced it.
 

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Correct, I've got the cheapo base CC which others have somewhat recently lamented here.
I much prefer the standard CC and jump though hoops every time I drive to select it (default is sticky to ACC). Lots of unwanted braking with the ACC, and even if I drove in stop and go freeway conditions that are really ACC intended use, the Niro system will not take you to zero and start again.
 
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