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Discussion Starter #1
I have a 2019 Santa Fe Ultimate 2.4L FWD, bought it back in April. ISG has been acting normal up until about 3 weeks ago, where it hasn't activated (turning off the engine) once in that period.

I know there is a long list of criteria, I pulled DTC codes (none) and then checked battery voltage and saw 12.3V yesterday. Didn't disconnect battery fully, but I assume parasitic loads are very small. Since it's an AGM battery, 12.3V puts it at SOC 50% or so-- which seems like a likely culprit fro ISG not kicking on, since if I remember correctly the activation criteria is > 68%. Next question is why is the battery level at 50% even after driving an hour on the highway.

I took it to the dealer as a walk-in, and they tested the battery-- CCA's were fine though charge level was 50%. It passed as Good, so there wasn't much more they could do without holding the car for a few days for a diagnosis.

I checked the battery after driving another hour or so today, 12.3V as well. When idling after a cold start, voltage observed at the terminal was around 14.5V, so it seems like the alternator is working fine as well. Some more searching online, and I ran into a post on talkhyundai.com that the alternator management system (AMS) controlled by the ECU will avoid charging the battery unless it really needs to to save mpg, except opportunistically when decelerating. Thus, the post said, it's possible that if driving habits are shorter trips, the AMS will allow the battery to settle at a lower charge level, below the threshold for ISG to activate.

I did change my driving habits ~2 months ago from regularly driving on the freeway to only driving on the freeway a couple times a week (girlfriend moved in, she previously lived about 45 minutes away), though I'd still estimate ~20+ miles of a driving most days, but more 30-45 mph and stop lights. So, it seems possible that not getting as much regular charge on the battery if the alternator is selecting not to kick in on these types of trips.

My question is: Has anyone else run into ISG not activating for weeks due to lower battery charges, or has anyone observed continual 50% or so battery charge levels?
 

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I have a 2019 Santa Fe Ultimate 2.4L FWD, bought it back in April. ISG has been acting normal up until about 3 weeks ago, where it hasn't activated (turning off the engine) once in that period.

I know there is a long list of criteria, I pulled DTC codes (none) and then checked battery voltage and saw 12.3V yesterday. Didn't disconnect battery fully, but I assume parasitic loads are very small. Since it's an AGM battery, 12.3V puts it at SOC 50% or so-- which seems like a likely culprit fro ISG not kicking on, since if I remember correctly the activation criteria is > 68%. Next question is why is the battery level at 50% even after driving an hour on the highway.

I took it to the dealer as a walk-in, and they tested the battery-- CCA's were fine though charge level was 50%. It passed as Good, so there wasn't much more they could do without holding the car for a few days for a diagnosis.

I checked the battery after driving another hour or so today, 12.3V as well. When idling after a cold start, voltage observed at the terminal was around 14.5V, so it seems like the alternator is working fine as well. Some more searching online, and I ran into a post on talkhyundai.com that the alternator management system (AMS) controlled by the ECU will avoid charging the battery unless it really needs to to save mpg, except opportunistically when decelerating. Thus, the post said, it's possible that if driving habits are shorter trips, the AMS will allow the battery to settle at a lower charge level, below the threshold for ISG to activate.

I did change my driving habits ~2 months ago from regularly driving on the freeway to only driving on the freeway a couple times a week (girlfriend moved in, she previously lived about 45 minutes away), though I'd still estimate ~20+ miles of a driving most days, but more 30-45 mph and stop lights. So, it seems possible that not getting as much regular charge on the battery if the alternator is selecting not to kick in on these types of trips.

My question is: Has anyone else run into ISG not activating for weeks due to lower battery charges, or has anyone observed continual 50% or so battery charge levels?
I’m totally with you, Kiddo. My ISG has not activated for weeks either. I suspect a low battery charge level.
 

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Mine has not activated for a few months. Some on these forums would like that it does not activate and I am on the fence so I have not taken it in.
 

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Discussion Starter #4
Battery was measuring at 12.3V, then 12.4V, and then this morning 12.15V, 12.15V again this evening (only drove around town a bit). Really not sure why battery voltage seems to be tanking... no issues starting the car yet, however.
 

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Battery was measuring at 12.3V, then 12.4V, and then this morning 12.15V, 12.15V again this evening (only drove around town a bit). Really not sure why battery voltage seems to be tanking... no issues starting the car yet, however.
You may have answered your own question.
 

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Discussion Starter #6
You may have answered your own question.
This wasn't a full day of town driving, just like about 25 minutes or so for the full day.

Measured battery level again this morning and about 12.05V now. Haven't tried turning it on yet.
 
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That will explain why my ISG is not working. I took my 2020 Santa Fe SEL to the dealer and they replaced my battery, but that was after telling me that a jump start on these AGM batteries will damage about 10% of the cells. I called Interstate Batteries and they confirmed what the dealer told me. So after dealer on Jan 6th put in a new battery with a full charge my ISG Stop/Start worked great for a couple of days. But I normally drive less than 10 miles per trip and only a couple of times per day. So Jan 6th new battery, then on Jan 15th, after ISG not working for almost a week, I put a battery charger on my battery and it reflected it was at 25% charge. (I forgot to measure voltage at that time). After 5hrs and supposedly it was at a full charge I disconnected the charger and turned on the headlights and measured 12.43v. With Headlights off I get 12.67v. So maybe I didn't let the charger charge long enough. Anyways the dealer also stated that once a week I should drive the car for 1 hour to charge up the battery. I'll put the charger on all night and see if that helps. Other then this I Love my Santa Fe. My charger is a Noco Genius 10. Noco verified that it will work on a 2020 Santa Fe.
 

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While I realize this isn’t addressing your question, is having the ISG not work really a bad thing?

While Hyundai’s implementation of it is pretty good, I still have concerns about the effect the system has on long-durability of parts like the starter motor (premature failure).

I will typically turn the system off when I get in the car, but I don’t experience a lot of stop-and-go traffic either.
 

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While I realize this isn’t addressing your question, is having the ISG not work really a bad thing?

While Hyundai’s implementation of it is pretty good, I still have concerns about the effect the system has on long-durability of parts like the starter motor (premature failure).

I will typically turn the system off when I get in the car, but I don’t experience a lot of stop-and-go traffic either.
I think most folks would like to see modern technology work, rather than get stuck in the last century. Atavists not so much.
 

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Discussion Starter #10
While I realize this isn’t addressing your question, is having the ISG not work really a bad thing?
More that it is indicative of either a failure in a component, a systematic design flaw, or poorly communicated operations-- I don't love the ISG on its own, but didn't mind it either.
 
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That will explain why my ISG is not working. I took my 2020 Santa Fe SEL to the dealer and they replaced my battery, but that was after telling me that a jump start on these AGM batteries will damage about 10% of the cells. I called Interstate Batteries and they confirmed what the dealer told me. So after dealer on Jan 6th put in a new battery with a full charge my ISG Stop/Start worked great for a couple of days. But I normally drive less than 10 miles per trip and only a couple of times per day. So Jan 6th new battery, then on Jan 15th, after ISG not working for almost a week, I put a battery charger on my battery and it reflected it was at 25% charge. (I forgot to measure the voltage at that time). After 5hrs and supposedly it was at a full charge I disconnected the charger and turned on the headlights and measured 12.43v. With Headlights off, I get 12.67v. So maybe I didn't let the charger charge long enough. Anyways the dealer also stated that once a week I should drive the car for 1 hour to charge up the battery. I'll put the charger on all night and see if that helps. Other then this I Love my Santa Fe. My charger is a Noco Genius 10. Noco verified that it will work on a 2020 Santa Fe.
After putting a full charge on my battery overnight my ISG worked perfectly the next day.
 

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While I realize this isn’t addressing your question, is having the ISG not work really a bad thing?
To me it is. I just paid a lot of a money for a new car. Erratic behavior contrary to design is unacceptable even if I never use the feature. I do find it useful when in town but it's really easy to turn it off for parking or stops you know will be very quick. When going to town, I simply feather the brake for the few country road stop signs I encounter.
 

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To me it is. I just paid a lot of a money for a new car. Erratic behavior contrary to design is unacceptable even if I never use the feature. I do find it useful when in town but it's really easy to turn it off for parking or stops you know will be very quick. When going to town, I simply feather the brake for the few country road stop signs I encounter.
You don’t have to feather the brake pedal to perform a proper, legal, stop at a stop sign.
 
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