Fixed a P0AA6 code

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Aug 14, 2019
Hello fellow Leafers,

I just fixed a 2015 Leaf with code P0AA6 "EV/HV Hybrid Batt Volt Sys Isolation".
TLDR: It was the 12V battery ground harness. Too much rust in the connection it seems.

Purchased the car with the problem, figuring I could surely fix this.

First of, I followed the service manual instructions, and got to measuring insulation resistance in the harnesses and AC compressor.
After that step, the car now throws a new code! Interlock issues!
I surely misconnected a connector, right. I go and redo the connection, code comes back.
I leave the car at that, telling myself I will need good contact cleaner and a way to make sure I did not damage a connector.

3 weeks later, I go back to the car. I forgot my OBD2 plugged in, so the 12V is completely discharged.
I proceed to plug a charger, then the car does all sorts of weird thing as the voltage rise slowly, so I disconnect the battery terminals and, since I must wait, proceed to clean them up. I notice the GND wire is very corroded, and disconnect/sand/clean/reconnect all the connection points.
After the battery is charged enough I plug everything back, clear the codes, and... it works.
I'm looking at the dash telling "ah ah, you can put the codes back, I get it."... but no!
It's been a week now and I everything is smooth sailing.

So, lesson learned here: the service manual tells "make sure 12V is above 12.5V", but nowhere ask to check for connections. It assumes that the 12V and HV batteries are firmly connected to the chassis gnd domain. Seems that if your 12V is not, then it can throw that isolation fault.

When I was initially researching this, I found many great advices, but not this one.
So I felt compelled to share it here, juste in case someone has the same issues in the future!

Thanks for reading, good luck!
Quick update, I was terribly wrong.
My issue was due to the Battery Connectors; the aluminium block behind them was flaking off due to corrosion, and some oxidized aluminium and moisture crept into the battery, touching the connectors high voltage pins.

I have made a very bad video about the work to change the block and clean the connectors.
You are a brave man working around all that high-voltage equipment without insulated gloves/tools!
I can't imagine how that damage occurred since (it seems) the case was "sealed". Was it immersed in water??
Impressive doing all that work by yourself...and filming the whole thing!