2017 BMS Question and Loud "Bong" Noise at Altitude

[SLC17Leaf]

This is my first post on this forum. Thanks in advanced for all the info, help and advice!

We purchased our leaf new in 2017 and it now has just over 54k miles. We're down to 9 bars on the battery SoH indicator. We rarely rapid charge with level 3 and most of our charging is overnight on the level 1 charger at home. Because we don't have a practical way of limiting the charge overnight we do sometimes hit 100%. We live in Salt Lake City, UT where temps in the summer are in the 90's for a couple months. We do get some days in the low 100's. Winters typically get down to the 20F-30F range overnight and we can get a few days here and there in the teens. Occasionally we get a few days in the single digits.

The car was used for a daily 4-5 day/week commute of about 50 miles round trip pre COVID for about 3 years. The commute climbs about 2000 feet over a 25 mile distance. When we hit about 5500 feet above sea level, there's a noticeable "bong" noise that sounds like someone kicked a steel drum. It happens at the same point on the commute, within a mile or so. It doesn't seem to make a similar noise on the return trip on the way back down. I'm guessing this sound is the result of a sealed battery compartment expanding due to the gain in elevation. Has anyone else experienced this and could it be a problem? We've mentioned it to our Nissan service department and they pretty much dismissed it and said it must be road noise. It's definitely not road noise.

The other issue we've been having over the last several months is the SoC indicator will suddenly (within 15 seconds or so) drop a couple bars and then most of the time will come back up a couple bars again. If we're around 45-50% SoC, it will sometimes go into the "turtle" mode. This happens mostly in the cold when going uphill at around 50-60MPH. Since it drops 30-40% within 15 seconds and over about 1/4 mile, it's not a true loss. Especially since it comes back up to nearly the same amount in about the same time. This wouldn't be too much of a problem if the car didn't go into turtle mode. Is this a problem with the battery or could this be a problem with the BMS? Or Both?

We got a video of this happening and gave it to our local Nissan service people. They think it's a problem with battery. Also, they think the battery degradation down to 9 bars SoH at 54k miles is excessive. The service department wants to replace the battery since they don't know how else to fix the problem, but Nissan is pushing back. The car has been with them for over a week and seems to be stuck in purgatory until they resolve their internal disputes. Is there anything else I should consider at this point?

Thanks again!

 

[LeftieBiker]

Welcome to the forum. The 30kwh battery in your Leaf has a known problem with degradation. Nissan issued a free software update for the Battery Management System (BMS), claiming that it was simply a programming error. It turned out that while some of the 30kwh batteries showing excessive degradation do just have a programming error in the BMS, it appears that many or most of them do not - it is in fact excessive degradation. Once your car loses one more capacity bar - AFTER having the BMS updated - to 8, then it is eligible for a free 40 kwh battery, because the 30kwh battery is no longer made...

In your case, however, I think that your battery ALSO has one or more defective cells in the battery. Once this is confirmed, if this is the case then you are eligible for a free 40kwh battery NOW. Confirming defective cells is both easy and difficult. Easy because the LeafSpy Pro app, paired with a suitable onboard diagnostic port ("OBDII") reader like the one in my signature, will show defective cells in its graph-like voltage histogram. Difficult, though, because Nisan doesn't recognize LeafSpy data as valid, even though LeafSpy uses the car's own BMS readings to get its information. They require that the car have shown error codes, called "DTCs". Has your car had the master EV Warning light come on, and/or displayed any error messages? Any such messages are stored by the car. One warning, though: if you use LeafSpy Pro, be aware that the app can both display and ERASE such messages. Don't do that... If no error codes have been thrown despite the car "Turtling," then you may be able to produce them by driving up a steep hill, with the state of charge below 30% or so. This load will cause voltage "sag" in the battery, and any weak cells should drop low enough in voltage to cause the BMS to activate Turtle Mode. Be careful. If this works but produces no error codes, then you need to do it again - with a Leaf-Certified Nissan technician riding along. Good luck!

As for the loud "BONG"? I haven't heard of that happening, but I tentatively agree with you on what may be causing it. The battery case is large, partially empty, and sealed to prevent water ingress, so it's a likely candidate.

 

[GerryAZ]

I agree, the symptoms described indicate weak cells and the fix is a new battery which should be under warranty. The battery case is sealed, but has vents that allow for gradual pressure change. I suspect your climb in altitude is rapid enough to change the pressure faster than the vents cans handle so the battery case expands. I doubt that it will cause any other problems (besides noise) and doing something to the vents could jeopardize the water-tight battery case.

 

[SLC17Leaf]

Ok, thanks for the replies! Your descriptions sound consistent with what is happening. I'm not sure about the error codes but I will ask the local service techs to check. I will also confirm that the BMS update has been done, although I'm pretty sure it was done a couple years ago. If there are no codes stored, I will do as you suggest and try to trigger them by driving under those conditions.

It sounds like everyone in on the same page with respect to the battery problem, except for the people at Nissan who can authorize a battery replacement under warranty. At this point there are three entities within Nissan who are involved with the resolution of the problem, our local service techs, the corporate technical department and the Nissan Consumer Affairs department, who specialize in Leaf issues. All seem to agree that the battery will be replaced under warranty at some point, but it's a matter of when. We've lost 2 bars of SoH within the last 12-13 months. So, I suspect it won't be long before we hit 8 bars. Certainly it will happen within the 100k miles and 96 months. We'd be more than happy to wait for the car to hit 8 bars SoH since we could put off the replacement a little longer and buy more time with the overall useful lifespan of the car. However, the sudden drop in SoC and turtling could leave us stranded on the side of the road. Also it's kind of a "bird in the hand" scenario.

I won't be concerned or take any action with the "bong" noise. I just waned to see if anyone else experienced this and make sure it isn't potentially damaging anything. I'm glad you both confirmed my thinking on that.

I'll keep updating as we learn more and there is progress towards a resolution.

Thanks again!

 

[SLC17Leaf]

So our local Nissan service department gave us the car back after having it their shop for almost 8 weeks. The service techs have been in communication with the Nissan engineers and had been trying to recreate the problem and get an error code. They were unable to recreate the problem. The service rep wanted us to drive it and bring it back ASAP when we had the problem again without turning it off, so they could scan it. I took the car for a drive on Friday morning and was able to get the car to go into "turtle mode" after driving for less than 10 minutes. I then drove it straight to the service shop without turning it off. The car went out of "turtle mode" but it did not generate any code. The service reps said that the car should have thrown codes if it went into "Turtle mode" I did get a GoPro video of the dash with all of this happening, which I submitted to the service rep. So they now have 2 videos of this problem occurring. I've included a youtube link for the video.

The car was basically in purgatory for 8 weeks without any resolution or fix. Our local service guys want to replace the battery because they're pretty sure there are defective cells, as you all have guessed as well. Nissan has yet to authorize the battery replacement, and have been pushing back on the service guys. No one has offered another solution/action to resolve the problem. This has been a very frustrating experience and I'm shocked at how poorly Nissan has dealt with acknowledging and resolving the issues. Nissan's support and knowledge base for their Leaf seems to be quite deficient. I'm guessing they have little incentive to develop a good diagnostic system for the Leaf, as it would likely lead to them having to replace more batteries. Instead it seems they want to fight with replacement tooth and nail. Is this typical in dealing with Nissan for Leaf problems?

I guess we'll have to continue to wait for our service guys to battle it out with Nissan engineering/corporate. We can keep trying to get the car to generate error codes. However, I'm not optimistic that it will since it has had this issue for sometime with multiple occurrences without generating any error codes. It seems that in addition to the battery problem, there's a system communication problem as well.

Thanks for all the input and support!

Here's the link for the video. The car goes into "turtle mode" and warns "Power is limited" just after the 2:45 mark in the YouTube video.

https://youtu.be/DTccCQV-i0E

 

[jlv]

Interesting that the SOC drops from 60% to 50% when the "Power is limited" shows up... which certainly points at some bad cells. In fact, the SOC was dropping very quickly.

 

[SLC17Leaf]

I've had the SoC drop from around 60% down to under %20 in less than 20 seconds. It will then come back up even faster when there is less load on it. I'm gonna try like hell to get it to generate DTCs, since it seams thats the only way Nissan will fix the car. I'm just not crazy about intentionally driving my car to failure on the highway, or stranding myself in the mountains in winter or pushing the accelerator to the floor on open roads where there are many hazards out of my control.

 

[SLC17Leaf]

Interesting that the SOC drops from 60% to 50% when the "Power is limited" shows up... which certainly points at some bad cells. In fact, the SOC was dropping very quickly.

I was just poking along on the highway at maybe 60mph on a slight uphill, about 7 minutes into the drive. It wasn't even that cold out, maybe 20F or so.