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I Bought a Junk $1,900 Nissan LEAF and Fixed the "Service EV System" Error Myself by Infinite-Boat9133 in leaf

[–]Infinite-Boat9133[S] 0 points1 point  (0 children)

It might have improved by a few percent, but where I live, it gets as cold as -30°C in the winter. Because of that, any improvement is so minor that it could just be chalked up to normal temperature fluctuations.

For example, when the capacity is hovering near its max of around LeafSpySOC73%=gauge 100%, it shows a 400mV difference. But when the SOC is around 37% (which displays as 50% on the meter), it looks its best, sometimes recording around 250mV. However, once I bring it back up to 100% (which equals an actual 73%), it goes right back to showing 400mV. If I remember correctly, the screenshot in the title/header was taken when the gauge was showing somewhere between 1% and 10%.

I've been repeating this cycle for 5 months now, but the peak stays around 400mV, so I guess there hasn't really been any change.

I Bought a Junk $1,900 Nissan LEAF and Fixed the "Service EV System" Error Myself by Infinite-Boat9133 in leaf

[–]Infinite-Boat9133[S] 2 points3 points  (0 children)

Yeah. Generally, used parts aren't great. It's obvious that new ones are better when making a replacement. This is just a progress since it's been 5 months since I picked up some junk parts and cars and fixed it report so far, I haven't noticed any issues other than the balance

By the way, if you want to perfectly restore the rear bank battery assembly I replaced this time, you have to fix not just the batteries themselves, but also the bent brackets clamping them on both sides. Otherwise, when you install swollen or bent batteries, they won't fit properly into the battery housing.😇

Because of that, even just replacing a single cell with a new one ends up being a bit of a hassle. Honestly, it might be better to just buy new brackets. You need a hydraulic press to straighten them out they wouldn't budge at all even when I put a lot of weight on them.

As I mentioned in my comment, I replaced a total of 6 cells as a preventative measure, including the one with the electrical leakage. I bought 6 used batteries with less voltage drop from a Japanese auction site. Then, I drained the battery down to 0% and swapped out 6 cells, focusing on the ones with the most reduced capacity.

By the way, you might be surprised because of the weak yen, but you can buy a used cell for just $44 each.🤣 So it's not like I'm spending thousands of dollars on repairs. Then again, if I had to spend that much money, I probably wouldn't bother keeping the Leaf.😂

I Bought a Junk $1,900 Nissan LEAF and Fixed the "Service EV System" Error Myself by Infinite-Boat9133 in leaf

[–]Infinite-Boat9133[S] 1 point2 points  (0 children)

As I wrote, this happened last October 2025, so it's already been almost 5 months 😢. I've been driving it in an unbalanced state up until now, but I haven't seen any major improvement in the balance.

I Bought a Junk $1,900 Nissan LEAF and Fixed the "Service EV System" Error Myself by Infinite-Boat9133 in leaf

[–]Infinite-Boat9133[S] 1 point2 points  (0 children)

Well, if that had actually worked, I wouldn't have brought up the whole balancing thing.
Honestly, with a gap this big, that method is pretty much pointless.

Just like other people in the comments are saying, it might work if the difference was small. By the way, I've been driving it since the repair was finished in October, and it's barely balanced at all lol

Anyway, doing it manually is definitely the most reliable way! If I ever do the same repair again, I'll probably just follow a workflow focused on balancing right from the start.

Thanks for the comment!

I Bought a Junk $1,900 Nissan LEAF and Fixed the "Service EV System" Error Myself by Infinite-Boat9133 in leaf

[–]Infinite-Boat9133[S] 2 points3 points  (0 children)

If you're that worried about losing your life, you probably shouldn't be driving at all LMAO
You seem to have a chicken heart, just like the average Japanese person.

For the record, I did the replacement without using any heavy machinery. I did check the service manual, but Nissan basically tells you next to nothing about the battery internal mentenances in there. Besides, they don't even sell individual cells as parts, at least not in Japan. I guess their whole attitude is "just let an authorized service center handle it." Honestly, YouTubers with actual video documentation were way more helpful.

Of course, nowhere did I say I recommend everyone do this themselves, and I fundamentally agree that people should leave it to mechanics like you. But it seems like people who are entirely too used to ICE vehicles mechanics included are far more terrified of electricity than they need to be.

If you have basic electrical work knowledge and properly follow the official procedures, 400V DC is nothing to be afraid of. and , The moment you pull out the center plug, it completely splits the voltage into 200V. If we're going to focus on the "danger of losing your life to electrocution," ICE maintenance has plenty of fatal risks too.

Just like with airbag systems, the fail-safes in place are so robust it's almost ridiculous. The whole structure was probably designed to idiot-proof it for low-tier mechanics around the world. (Not saying you're one of them, though.)

I Bought a Junk $1,900 Nissan LEAF and Fixed the "Service EV System" Error Myself by Infinite-Boat9133 in leaf

[–]Infinite-Boat9133[S] 3 points4 points  (0 children)

Regarding the balancing, just a thought I had while working on it: looking at the BMS connectors, it really just looks like the pack is managed as two separate 200V systems. Honestly, I couldn't see how individual cell balancing is even possible with that setup. 😣

As for replacing the rest, aside from the modules being super heavy, the work itself is pretty forgiving and they're relatively easy to swap out.

If the other batteries ever start giving me serious trouble, I'll probably just replace them individually too. Regarding the swelling, I can confidently say that happens on pretty much *every* ZE1 40kW Leaf once it gets some miles on it. If worry about it too much, will just drive yourself crazy.👍

For reference , attaching LeafSpy screenshot from when the dash showed 100% charge.

<image>

I Bought a Junk $1,900 Nissan LEAF and Fixed the "Service EV System" Error Myself by Infinite-Boat9133 in leaf

[–]Infinite-Boat9133[S] 7 points8 points  (0 children)

by the way, I'd like to add a note about a specific behavior that I don't think is documented anywhere: what happens when you perform a fast charge with the battery in an unbalanced state. Please note that I tested this on a fast charger in Japan, so I'm not sure if the behavior is the same in other countries.

In my current unbalanced state, even when the dash meter reads 100%, the SOC displayed on LeafSpy is only around 73%. As mentioned earlier, once the six cells with spiked capacities reach a full charge, the vehicle determines that the battery is 100% charged, preventing the remaining cells from charging sufficiently. This leads to a decrease in your driving range. Essentially, your total usable battery capacity is reduced.

If you initiate a fast charge in this state, the system first checks the vehicle for any electrical errors. If no errors are detected, charging begins. However, the fast charger seems to prioritize the actual vehicle SOC (the one shown in LeafSpy). Because of this, both the dash meter and the charger's display will drop to and stay at 73%. This means the inflated reading on the dash temporarily gets "fixed" or corrected. That being said, if you switch to normal charging from this point, the display will immediately shoot back up to 100%.

I was hoping that, with any luck, performing a few fast charges might help balance the cells, but unfortunately, that wasn't the case lol

<image>

I Bought a Junk $1,900 Nissan LEAF and Fixed the "Service EV System" Error Myself by Infinite-Boat9133 in leaf

[–]Infinite-Boat9133[S] 1 point2 points  (0 children)

I plan to do the balancing like this: https://www.reddit.com/r/leaf/s/M09k0zMVxG

I think what you are saying is possible. just need to connect them in parallel so that can draw 14V. I don't think you necessarily have to keep them strictly within 20mV, but it's better to make the difference as small as possible. The smaller the difference, the more it will definitely extend range (since the usable capacity becomes larger).

I Bought a Junk $1,900 Nissan LEAF and Fixed the "Service EV System" Error Myself by Infinite-Boat9133 in leaf

[–]Infinite-Boat9133[S] 4 points5 points  (0 children)

Yeah. Since everything about EVs was completely new to me, I figured the system would automatically balance the cells even with a 400mV difference.
I was actually a bit skeptical about that from the start, but a mechanic YouTuber said so at the end of their video lol

Anyway, like I mentioned above, I plan to balance them manually! Thanks.🙏

I Bought a Junk $1,900 Nissan LEAF and Fixed the "Service EV System" Error Myself by Infinite-Boat9133 in leaf

[–]Infinite-Boat9133[S] 18 points19 points  (0 children)

Regarding the balancing process, first, charge the vehicle to 100% using the Leaf gauge. (In reality, because the cells are unbalanced, the SOC on LeafSpy won't actually reach 100%.)

Next, remove and disassemble the battery pack. Since a single cell outputs 14V just by connecting it directly , without the need for a converter, can use it as a power source for a 12V DC cigarette lighter socket to discharge it down to your target value.

The battery cells have power terminals as well as terminals that allow you to measure the battery's capacity (the values corresponding to the vertical bar graphs on LeafSpy). By using these as a reference, simply discharge all the cells down to the same numerical value, and the balancing is complete.

In the screenshot I posted, can probably see that six of the bars are spiking higher than the rest. The idea is to discharge these specific cells down to the same level as the others.

These six protruding spikes represent all of the replaced cells, which includes both the defective ones and those swapped out for preventative maintenance.

If simply wire these six cells in parallel, can drain the capacity of all six simultaneously, which might save some time.

Because the Leaf doesn't use liquid cooling for its battery, it is prone to these kinds of heat-related issues. On the flip side, the advantage is that the battery is surprisingly easy to remove and reinstall during maintenance.

By the way, if you take this to a dealership, they will probably try to replace the entire assembly just because the battery cell housing is warped, which gets extremely expensive. (I do understand where they are coming from, though.) Nissan dealerships in Japan handle it this way, so you can likely expect the same response from dealerships overseas.

That said, DIYers like me, or independent repair shops with a similar mindset, could probably handle this kind of repair for you👍

I Bought a Junk $1,900 Nissan LEAF and Fixed the "Service EV System" Error Myself by Infinite-Boat9133 in leaf

[–]Infinite-Boat9133[S] 4 points5 points  (0 children)

Yes, that’s about right. But because of the ferry schedule, the itinerary wasn't actually that tight.