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BMS reset proof for dealership

Posted: Sun Mar 17, 2019 11:04 am
by Astros
Yesterday I was helping an older friend shop for a new (to him) car, and so I wanted to show him a Leaf to compare with the Kia Soul and Honda Fit he was looking at. He was skeptical, but as soon as he drove it he was sold. Despite everything I had said about the Leaf in the past, he was still expecting a sluggish golf cart.

So, that was all fine, and after downgrading from an 2017 SV to an 2017 S we were able to get well within his budget, but I also was concerned about the battery. I hooked up LeafSpy, and read 79.16 aHr, 99.6% SOH, 92.04 Hx with 24,000 miles, 80 L3 and 363 L1/L2s. The nearly 100% SOH made me concerned that the BMS had been reset, so I insisted on talking with the service manager. Here things got frustrating, because she adamantly claimed that it was absolutely impossible to reset the BMS without replacing the battery, and anything I had heard to the contrary was false.

In the end, I decided that this Leaf was fine for my friend, since the 5% degradation shown by the aHr was probably realistic. But, does anyone have suggestions for good evidence I can point stubborn Nissan people to in the future? For those in Washington, this was at Tacoma Nissan.

Re: BMS reset proof for dealership

Posted: Sun Mar 17, 2019 11:36 am
by SageBrush
The dealership is wrong.

Sorry to say, I suspect you gave your friend poor advice.
The way to handle these suspect cases is to either match miles driven to SoC fall over a longish test drive, or to head to a ChargePoint EVSE and match kWh delivered to SoC gained. Figure that ~ 12% of kWh delivered are losses that do not make it to the battery. If using a ChargePoint try to charge for at least an hour, preferably two.

These calcs are not exact but they are more than good enough to identify a battery reset.

Re: BMS reset proof for dealership

Posted: Sun Mar 17, 2019 7:30 pm
by GerryAZ
The AHr and SOH numbers are probably correct if the car has lived in the cool Pacific Northwest for its entire life.

Re: BMS reset proof for dealership

Posted: Mon Mar 18, 2019 8:04 pm
by brunohill
Extract from Nissan Service Bulletin

IMPORTANT:
DO NOT “READ & WRITE” any Li-ion Battery Controller (LBC) data to the new HV
Battery Pack assembly.
Writing the old HV Batt ery Pack LBC data to the new HV Battery Pack assembly will
cause the vehicle to read only 8 bars of capacity and will require the LBC to be
replaced.

Re: BMS reset proof for dealership

Posted: Mon Aug 12, 2019 5:22 pm
by valem
SageBrush wrote:
Sun Mar 17, 2019 11:36 am
The dealership is wrong.

match kWh delivered to SoC gained. Figure that ~ 12% of kWh delivered are losses that do not make it to the battery.
Can you please elaborate on this? How do you match kWh to SOC to determine BMS reset?
And dash SOC or Leafspy SOC ?

Thanks

Re: BMS reset proof for dealership

Posted: Mon Aug 12, 2019 5:29 pm
by LeftieBiker
The big problem here is that there is no established, recognized-by-Nissan way to prove a BMS reset to a Nissan dealership. It appears that they can establish the actual capacity using their diagnostic equipment (this is a requirement for warranty replacement of a pack) but they won't do that as a favor, service, or for any other reason than a warranty claim. You can show them KWH in vs miles driven, or whatever you like, but you've already seen what they will say (and this often represents what they "know" as well). The only thing that stands a reasonable chance of being counted as proof is a Leaf losing TWO capacity bars in a short time. Not one, two.

Re: BMS reset proof for dealership

Posted: Tue Aug 13, 2019 10:20 am
by alozzy
That, and common sense really. The old adage "If it sounds (seems) too good to be true, it probably is..." applies to used Leaf purchases. Knowing where a used Leaf was originally sold, and where it spent most of its time, is a big factor - as we all know, heat is the biggest enemy of the LEAF packs...

For instance, if someone is looking to buy a used 2015 LEAF, finds one that LeafSpy reports has >90% SOH, and that car spent most of the time in SoCal or Arizona (or some other hot place) then a BMS reset is likely. But a PNW 2015 LEAF would very likely still have >90% SOH.

You could take a risk on an outlier that seems exceptionally good, but I personally wouldn't.

Use a Google search to find other posts on range tests - there are plenty already in these forums:

range test site:mynissanleaf.com