Sudden Turtle Mode in Very Cold Weather

[rogersleaf]

It would be helpful to the community if someone uses LeafSpy, while the car is in turtle mode, to see if there's a large cell imbalance.

My own event a couple nights ago didn't completely turtle, but was heading on that trajectory pretty quick. Today was another near-0F commute with high teens on the return trip. I ran leafspy this time while driving to see if it would act up again today (it did not) and to watch cell balance and actual battery temps.

Think I'm seeing the problem now... Battery temps today were relatively low (3 segments on dash) and showing in the low-to-mid 30F's on leafspy, SOC was under 40%. The cell balance becomes very unbalanced (say in 50+ mV range) if the car is pulling higher power loads such as @ 3KW to heater and pulling a grade at expressway speeds. Under those conditions, certain cell pairs (#50 or 51, and a few adjacent cells) basically drop off the bottom of the leafspy voltage graph. Once the battery temps warmed slightly (@ 4 segments & in 40F's on leafspy) or the load dropped, the cell balance leveled out and looked very normal. In hindsight, the events from a couple night ago was along the same pattern. The SOC cratered when pulling a substantial long expressway grade and then recovered when I headed for the exit.

[LeftieBiker]

It looks like my initial reply was incomplete. There is a third possibility, and it now seems likeliest: a cold-soaked battery with cells so close to the low voltage cutoff that they reach it without the motor being under much more load - they just can't provide power as well as they normally would, and slowly lose ground, so to speak.

[alozzy]

Now the trick will be to convince Nissan that those cells are weak and need to be replaced...

[rogersleaf]

I had the same thought about proving a battery defect while watching this happen. Doubt this throws any fault codes and would be difficult to reproduce at this point in the battery warranty life. I do still have 41K miles of warranty so who knows.

This behaves a lot like the battery decay in my old iPhone SE. If the phone was in a pocket and outside in Winter cold, sometimes the SOC would abruptly crater. If rebooted the phone, the SOC would recover some but relatively obvious it wasn't happy. Then Apple stepped in and said my battery was starting to fail.

[alozzy]

I sure hope you get somewhere with Nissan, this shouldn't be happening with a barely 3 year old Leaf.

[SLC17Leaf]

I've had the same sudden drop in SoC, turtle mode and power limited when driving on the highway at lower temps. This winter it happens every time I drive on the highway with even a slight sustained uphill grade when the battery temp is 4 bars or less. I've had it happen with SoC ranging from 30%-60% and battery pack temps as warm as 48F. We've been going back and forth with the local Nissan service department, Nissan engineering and Nissan consumer affairs for a few months now. No resolution yet. We haven't gotten any DTCs yet when this happens. The car has been completely unusable for highway driving when the battery temp is 3 bars or less, unless it's flat enough to allow the battery to warm up before there's any uphill grade.

This morning the Nissan techs hooked up a diagnostic computer to the OBD2 and sent me off on a drive to try to catch the problem and get the data. I had about 40% SoC and a battery pack temp of 38F. It dropped SoC, turtled and went into power limited after a couple miles on the highway with a slight sustained uphill. I limped back to the dealership and the tech pulled the data to send off to Nissan engineering. They didn't find any DTCs related to the problem. Now we need to see what the Nissan engineers say. My service guys are acknowledging that the car is failing to perform basic functions and is creating unsafe situations, so they're continuing to fight for us. But we'll have to see how far they can get with what they have for information. Also, the tech seems pretty motivated to determine a course of action because he's dealing with 4 other Leafs with the same problem. Once spring comes, I guess we put it all off until next winter or we loose another SoH bar, from 9 to 8.

It's been pretty warm here in norther UT this past week but it's supposed to get cold again next week. So I'm going to try to get it to generate some DTCs when the battery pack temp is lower. I will also try to catch it with a screen record video on Leaf Spy.

The car is a 2017 with around 56k miles SoH is at 9 bars/72.48%.

[LeftieBiker]

Do you think that you could find out whether the other 4 Leafs with this issue are also 30kwh?

[SLC17Leaf]

Do you think that you could find out whether the other 4 Leafs with this issue are also 30kwh?

I think he did say they were 16's and 17's, but I will ask again next time we talk. He did say that there was one other car this winter (not one of the other 4) with a 30kw battery that was having similar issues but it lost another SoH bar down to 8. They replaced it with a 40kW battery. He's hoping my car does the same. But at 72.48% SOH, it probably won't happen for several months. We've lost 3 SoH bars over the past 2.5 years. He said he hadn't seen the issue prior to this winter, then a rash of them (6 I suppose) came in this winter. 5 of those are unresolved. He's hoping these morning test drives with the diagnostic computer will give him a formula for repeating and resolving the outstanding cases.

[jjeff]

4 temp bars I could only wish, often this winter when I get in mine there have been NO temp bars 0F or colder and generally a pack temp of 0 or single digits

[BrockWI]

Yes, if ours did that at 4 bars we would really be in trouble, ours will do that with 0 or 1 bar of temp.