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Discussion Starter #1
Hi all, I've had little success with the dealer so trying my luck here!
My new 2020 Ioniq EV has started behaving very oddly and I'm hoping someone here has experienced the same thing or can offer advice.

When the battery is at 100% charge, I've noticed that within the first couple miles of driving the vehicle's throttle response is significantly impaired when pressing the accelerator. I'll be driving along, approaching a stoplight, and I'll release the accelerator to let the regen take over. This appears to work correctly, but when I apply new pressure to the accelerator I can feel the car fighting me. It doesn't want to accelerate. If I press the accelerator to the floor, the car will not deliver more power. This can be felt AND seen in the power delivery meter on the driver display cluster. Then, after a few miles, the problem suddenly stops and power delivery returns to normal behavior.

The only thing I've noticed is that it seems to only do this when the battery is at 100%, and once the charge drops to 99% or 98%, the vehicle behaves normally again. I thought it could be an issue with how the computer is communicating with the physical brakes, but it doesn't feel like the brakes are being engaged when this problem happens. It feels like the motor itself is just refusing to respond with full power.

I've been to the dealer and they claim to not see any errors from the ECU, but the problem persists.

I've attached a couple videos to illustrate the problem. Does anyone have any ideas?
 

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Red 2019 Ioniq 38 Premium EV
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The only thing I can suggest is that some EVs won't use regen when at 100% SOC, because they don't want to over-charge the battery. Can be disconcerting to expect the car to slow down, and it doesn't, forcing you to use the actual discs suddenly!

But there's always a margin at the top & bottom of the battery, and if you can regen while at 100%, are you starting on top of a hill and descending it immediately? If so, I wonder if Ionic is actually letting you over-charge to say 101% without admitting that it's doing so, but after that it knows it's in "danger-zone" as far as regen etc is concerned, and wants to protect the battery which is now right up against the very limits? So who knows what safety-measures may be kicking in.

Hard acceleration at that stage will warm the battery faster than gentle acceleration, and exercise it harder than a gentle cruise, so maybe they're simply restricting your range of choices while the battery is outside the "normal" working region 0-100% ? Kind of turtle-mode at the other end of the scale?

All I can suggest is do something to use a bit of battery at the very start, maybe heat the cabin to higher temperature initially, something like that? You can always give the rear discs a quick polish up by braking while in Neutral, that's actually a useful thing to do to stop them deteriorating super-fast through inactivity! Just a dab or two should shine them up nicely, and will use a tiny bit of juice doing so, as you recover any lost speed. I always do this after washing the car, or after a wet drive. Otherwise the rears can rust to bits while the fronts look perfect!
 

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Ioniq 2020 Premium SE
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When I first drove my Ioniq away from the dealers, I soon realised the regen wasn't working as it was on 100%, in fact it gave me a dash error message saying as much.
So trying for regen at 100% could def lead to some slightly strange behaviour. Haven't experienced it since but am rarely at 100% for long.
 

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I think I have worked out that - exactly as plugged-in recharging slows down hugely as the thing gets close to 100% - the BMS is doing the same for regen; i.e. extreme deceleration (regen) would try to dump more kW into the battery than the BMS thinks is "safe". So it refuses. The closer you are to 100% SOC, the less kW is allowed, and therefore the less effective regen (and thereby single-pedal driving) is. Real brakes needed.

This has nothing to do with acceleration though and I haven't seen any effect on that for being at or near 100%.
 

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Discussion Starter #5
The only thing I can suggest is that some EVs won't use regen when at 100% SOC, because they don't want to over-charge the battery. Can be disconcerting to expect the car to slow down, and it doesn't, forcing you to use the actual discs suddenly!

But there's always a margin at the top & bottom of the battery, and if you can regen while at 100%, are you starting on top of a hill and descending it immediately? If so, I wonder if Ionic is actually letting you over-charge to say 101% without admitting that it's doing so, but after that it knows it's in "danger-zone" as far as regen etc is concerned, and wants to protect the battery which is now right up against the very limits? So who knows what safety-measures may be kicking in.

Hard acceleration at that stage will warm the battery faster than gentle acceleration, and exercise it harder than a gentle cruise, so maybe they're simply restricting your range of choices while the battery is outside the "normal" working region 0-100% ? Kind of turtle-mode at the other end of the scale?

All I can suggest is do something to use a bit of battery at the very start, maybe heat the cabin to higher temperature initially, something like that? You can always give the rear discs a quick polish up by braking while in Neutral, that's actually a useful thing to do to stop them deteriorating super-fast through inactivity! Just a dab or two should shine them up nicely, and will use a tiny bit of juice doing so, as you recover any lost speed. I always do this after washing the car, or after a wet drive. Otherwise the rears can rust to bits while the fronts look perfect!
 

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Discussion Starter #6
Thanks so much for the replies!
@HandyAndy I think you're on the right track. When I try to use the regen paddle to stop the car and the battery is at 100% I get a beep and message in the cluster. Then the problem starts. But why would the car cut power delivery at that time? I mean, it literally won’t deliver more than about 50% power even if I put my foot to the floor. This can be seen in my videos. Seems like that could be rather dangerous in certain situations and it’s very startling while driving.
 

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Perhaps a cold battery combined with the regen limit? Maybe the BMS is just curiously engineered to limit power in and out of the battery when topped to brim. I would suggest in any case to avoid charging to 100% and limiting to perhaps 95% when the 100% isn't necessary.
 

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IONIQ Electric, SE (w/ CCP) 2018.
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I think it's as suggested by Andy above. When the car is at 100% and you try to use regen, that energy tries to go to the battery, and is rejected. Possibly though, the BMS might detect that the battery has been slightly overcharged due to that and has temporarily lowered the power threshold, hence on 50% power delivery.

Does the problem also occur if you just drive with the accelerator and brake pedal, or only when you use the paddles for one pedal driving. If so then then I think we can assume it's a protection against "overcharge" and you have two options. Charge to a lower SoC (most of us do anyway to reduce battery degradation - unless we need the full range of the vehicle for a trip) or don't try one pedal driving until your SoC has dropped to 98% or 97% after charging.

That said, you'd think that Hyundai could have told you all this, if they knew what they were talking about.
 
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What is the ambient temperature outside when this is happening? I know other cars restrict power delivery when the battery is cold. I think I have seen comments on the ID 3 forum indicating the power bar was only at 50% on cold mornings, also has been mentioned on MG ZS forum
 

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This looks like a bug to me. If the battery would be overcharged, the BMS' goal should be to lower the SoC and not keep it.
 

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Discussion Starter #12
@Fu Kin Fast I agree it seems like a bug. I've reached out to Hyundai to hopefully fix with a software update. My main concern is it could present a serious safety issue in certain driving situations.
 

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Yes, safety issue came also to my mind. That recuperation is limited when fully charged, is expected (other cars don't have it at all when fully charged), but that the power is limited seems weird to me. I only know limited power if the battery gets empty (experience from the e-Golf).
 

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Discussion Starter #15
@BillTheButcher I have regen set to level 3 in the menus and I'm honestly not sure why is says AUTO sometimes and sometimes AUTO goes away while driving. Is there a way to disable AUTO? The menus are honestly pretty confusing and I can't find that setting anywhere.
 

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Ioniq 38kwh 2020
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@BillTheButcher I have regen set to level 3 in the menus and I'm honestly not sure why is says AUTO sometimes and sometimes AUTO goes away while driving. Is there a way to disable AUTO? The menus are honestly pretty confusing and I can't find that setting anywhere.
AUTO is basically the smart regen, so if you approach some slow cars, or a junction or obstacle it automatically slows you down. Hold the right paddle to turn if off.
 

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Discussion Starter #18
Ok I’ve tested this issue extensively and here are reproduce steps to make the behavior happen. I’ve been able to consistently reproduce the issue, hoping others can do the same so I can move forward with Hyundai to get a fix.

1. charge battery to full (100%).
2. be sure smart regen is enabled and regen is set to level 3.
3. drive the car and use left paddle to bring car to complete stop.
4. system will beep and message will be displayed in driver cluster “regen braking not available, battery is fully charged” or similar
5. continue driving and notice that throttle response is impaired. pressure on accelerator pedal does not behave normally.
6. use right paddle to disable smart regen, then re-enable smart regen
7. feel that throttle response has returned to normal
 
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