So my issue is getting worse. My car is now going into turtle mode and power limited mode at high SoC (50-70%) and with a warm battery (5-6 temp bars). Previously, it was only doing this when the battery was 4 temp bars or less and a SoC of 50% or less. It's only doing this on the highway and uphill, but I turtles every time I drive up Parley's Canyon on I80 East from Salt Lake to Park City, UT. The drive climbs from around 4500ft ASL to 7000ft ASL in about 15 miles. If the battery is colder and a lower SoC, it will turtle on a slight uphill at highway speeds. If it is warmer and a higher SoC, it takes a steeper hill to Turtle. It has yet to set a DTC of any kind related to the drive system, despite my best efforts. I would have been content driving it as is through the warm weather and waiting for another SoH bar to drop (from 9 to 8) but it doesn't look like we're going to be able to do that now that it's happening every time on that drive, even with a warm battery.
My local Nissan Tech plugged in the Nissan Data logger to the OBD2 on three separate occasions and has me drive the car around for a few days trying to catch the data when the car turtles. I've had the car turtle multiple times with the Nissan Data Logger plugged in. The Nissan engineers have requested the data from the tech, to diagnose the problem. The Tech says they're mostly looking for cell deviation. He downloads the data and sends it to the Nissan Engineers. So far they've only come back and asked for more data, having not seen what they're claiming to look for yet.
One of the other four 30Kw leafs the tech is dealing with was turtling in a similar manner at the same point on 80 East up Parley's Canyon. They were able to see the cell voltage deviation on the logger and tried replacing the weak cells. The SoH of that car was also at 9 bars. Replacing the weak cells only made it worse according to the tech, apparently because the voltage deviation was high between the new cells they replaced and the existing with the new cells being higher. So, they ultimately replaced the entire pack with a 40kW.
I've been very happy with the effort our local Nissan Service department has put into trying to resolve this problem. They've definitely been going to bat for us and fighting the resistance from Nissan corporate.
The other thing I noticed today is that the battery temp is climbing faster than what I'd expect (or at least what I remember from before) when driving up hill on the highway. Today I started the drive at 4 temp bars and it climbed to 8 bars by the time I got the the top of the canyon. It was 44F ambient when I left and 40F by the time I got to the top of the canyon. Previously I've only seen 8 temp bars in the summer months or on the rare occasion we've had to Level 3 charge for a while when the battery was already a little warm.
Our tech wants us to drive the car for about a week with the data logger plugged in to catch as much turtle data as possible. His plan is to bombard the Nissan engineers with data. If they don't have a resolution after the engineers review the data, they're' going to elevate the issue to hopefully replace the battery. We've been dealing with this issue since November and there's been a considerable amount of time invested into resolving it. At this point I suspect when you factor in the value of everyones time and loaner cars, Nissan would have some out ahead if they just replaced the battery to begin with.
Our tech mentioned that the last two 40kW batteries he ordered took 2 months to get in. I jokingly (but not really) asked him if he could just order the battery now and by the time it comes in we'd loose another SoH bar. He said it's a huge pain to order a battery from Nissan and they don't list them in their parts system. Apparently there's an involved process and paperwork for a dealer to get a battery from Nissan. Nissan has tight controls on the distribution of the batteries.
We'll see what happens. Hopefully they catch something this time on the data logger. I'll update again when I have more info.