Another 12v Battery Drain Issue (Not TCU Related)

[Marktm]

Like most problems that arise from careless mechanics, it's very difficult requiring emphasizing;
1. The vehicle had no battery drain before 24 kWh battery replacement.
2. The BCM is integral to the functioning of the 24 kWh battery, e.g. it has physical wiring connections too it.
3. The Nissan repair manual's procedure for replacing the 24 kWh battery and each step needs to be reviewed as related to the BCM.

lorenfb;
A very interesting proposition that you are making as so many of us (Leaf owners) have had "battery drain" issues that seem to be highly specific to EVs. Being an ICE guy for decades, most "battery issues" related to a bad wire, a bad battery cell (usually) and very infrequently - a bad vehicle design related to new features not properly vetted (my Father-in-laws Lexus that required new batteries regularly even though he maintained "trickle" charging).

Is there a way to tell from LeafSpy data, DTCs, or any other analytics available to us ordinary folks that would help identify that a mechanic damaged such a critical electronic part after repair work? Just wondering.

 

[Marktm]

lorenfb;
BTW, I've anecdotally convinced myself that my regen brake surging is a result of the improper charging protocols on my FLA 12v battery. "Settled" voltages are in the range of 12.4 volts - much too low to maintain a healthy battery. IMO, trickle charging alone is not a good solution as it does not "mix" the electrolyte - need to use a 15 amp + charger - then keep it on a trickle charger every so often (once a month?).
So... it does seem these early Leaf 12 V system has some quirks - and possibly can be exacerbated by bad repair jobs on other electronic components?

Note that a low "settled" voltage can result in VERY low voltages when high amperes are stressing the 12V system.

 

[LeftieBiker]

FWIW, typical Leaf rest voltages for older Leafs run at about 12.4-12.6 volts. My 2018 Leaf, along with others that have been tested, actually is lower than that. (IIRC mine was 12.26.) It's a badly programmed charging system, but most Leafs don't have the surging, and most have low accessory voltages with the car off...

 

[lorenfb]

Like most problems that arise from careless mechanics, it's very difficult requiring emphasizing;
1. The vehicle had no battery drain before 24 kWh battery replacement.
2. The BCM is integral to the functioning of the 24 kWh battery, e.g. it has physical wiring connections too it.
3. The Nissan repair manual's procedure for replacing the 24 kWh battery and each step needs to be reviewed as related to the BCM.

lorenfb;
A very interesting proposition that you are making as so many of us (Leaf owners) have had "battery drain" issues that seem to be highly specific to EVs. Being an ICE guy for decades, most "battery issues" related to a bad wire, a bad battery cell (usually) and very infrequently - a bad vehicle design related to new features not properly vetted (my Father-in-laws Lexus that required new batteries regularly even though he maintained "trickle" charging).

Is there a way to tell from LeafSpy data, DTCs, or any other analytics available to us ordinary folks that would help identify that a mechanic damaged such a critical electronic part after repair work? Just wondering.

Yes, I would use LS to determine if there's a BCM fault code and what it is, as a minimum. Unfortunately, LS doesn't provide ECUs'
actual values which would definitively be insightful, as does the Nissan Consult tool does. All it takes to damage the BCM, or any ECU,
is a static charge from the traction battery to any ECU input, because a tech didn't follow a critical procedure.

 

[Nubo]

Curious as to how the BCM is consuming power. It monitors a crapload of switches and sensors to control accessories. One notable feature is "battery-saving mode", where it performs its checklist much less frequently. Didn't delve into it much past that, but there may be inputs that could be checked to see if the BCM's CPU is not getting the signals it would need to enter "battery-saving mode". If the CPU were fried, I'd expect more serious problems than a slow battery drain though I guess it could be "selectively fried".

 

[lorenfb]

Curious as to how the BCM is consuming power. It monitors a crapload of switches and sensors to control accessories. One notable feature is "battery-saving mode", where it performs its checklist much less frequently. Didn't delve into it much past that, but there may be inputs that could be checked to see if the BCM's CPU is not getting the signals it would need to enter "battery-saving mode". If the CPU were fried, I'd expect more serious problems than a slow battery drain though I guess it could be "selectively fried".

1. It's unlikely that a total failure state, "CPU were fried", of the BCM exists, since it's somewhat fully functional.
2. It's fairly easy to determine any vehicle's ECU's sleep-mode current by measuring the #30 power (the continuous 12V input),
once the systems enter the sleep-mode. Obviously, one would need the wiring diagrams and access to the ECU's connectors.
3. All that would be required to prevent an ECU from entering its sleep-mode would be a damaged sensor input "hanging" its processor.
4. As previously mentioned, having access to the Nissan Consult diagnostic tool and reading actual input values could
be very helpful in diagnosing the BCM. If there were non-resetable faults, e.g. a sensor input, but that sensor and its wiring
were OK, then one could conclude that a BCM input was damaged.
5. If the BCM ECU were re-flashable, one could attempt to re-flash it using the Nissan Consult tool. It's possible a transient power
situation could have corrupted the processor's flash memory.