P0AA6 w 526 and 612 : I don't think it's the battery - what next?

I have been lurking on PriusChat for a while, but running into an issue I need help with.

Daughter's 2009 prius with about 180K on it threw the P0AA6 code last week. Assuming it was a leaky module, I:

- pulled out the traction battery
- took off the bus bars and checked each module.
- charged the 12v battery to 100% just in case (it's about a year old, and was sitting at 12.6v when tested

there is no current going to the case from any module. all modules look perfect. No modules are discolored, case is clean, dry and looks great.

The bus bars were kinda corroded, so I took them out and threw them in a brass polisher and they look brand new now.

Each cell tested almost exactly 7.5 volts. The largest variation was .2. I had a few 7.48, a couple 7.51, but largely they're all hovering right around 7.5v. I tested them all several hours later and voltage was the same.

cleaned the little silver terminals that sit over the bus bars best I could and put it back in.

It immediately threw the code again. I can only get it to drive by pulling out the connectors to the 12v battery and waiting a sec.

Took it to a shop today, they charged me 150 bucks (OUCH) to pull the full codes and run a diagnostic. They got

P0AA6 and codes 526 and 612. They also said the hybrid battery was at 0% and needed to be replaced. they quoted about 3500 to do that. Oddly, when I took the car in, it was almost fully charged on the onscreen display.

I told them that I had checked the battery and it seemed fine, and the tech said maybe the ECU was bad.

I drove the car home and the Hybrid battery was down to 2 bars, and they were purple. When I left it had almost full charge and was blue. That was weird. Almost like they discharged the battery checking it or something. I drove it home and the battery charged up, and right as I got home it threw the codes again.

I'm going to pull the battery out again, what do I do next? Just replace the ECU and see if it fixes it? I'm going to look at the relays and cable, and order a megohmeter. I found this link in another thread and will follow this, but need to order a megohmeter first. I just have a normal one:

145252_2006_Prius_RM_-_P0AA6.pdf

should I just grab and ECU and go from there? What else is likely if it's not my battery? I'm going to do the voltage test right now where you test off the safety plug to the case and see what that says.


She's got to head back to college in 2 weeks and with the price of gas, replacing a fuel efficient car is REALLY expensive right now, so I'm doing my best to help her out with it. I'll get pictures of the case when it comes back out.....

 

tested lower bolt on the safety plug to the battery case and it's showing 49v pretty steady. according to the youtube video I saw, this means there is s leak in the battery, just not sure where. Could the ECU leak to the safety plug?

When I checked the cell pins to the case, none of them showed any voltage. All were open circuits. So I don't think it's the cells themselves.

 

I may be missing something. Post 14 talks about new modules vs old modules. am I looking at the wrong post?

 

I think I have to have a megohmmeter for this for sure. ordering one now

 

I did this test detailed by this guy on YouTube

This is the test from case to case, no resistance


Test from front cable terminal to the battery case. No leakage


Test to the rear post, no leakage from that part of the battery


But then very oddly, I tested the lower, long cable from the end of that cable to the case and it showed low resistance and was bouncing around, so according to that test, there's a leak here somewhere




Questions;
1) is this a valid test?
2) I'm thinking of isolating this cable and testing it's resistance or just replacing it.

Good plan or bad idea?

 

it's not a vibratory polisher. it's a tumbler exactly like a rock polisher. In reloading often referred to as a "wet" tumbler because you throw your brass, the steel pins and fill it half full of water and lemishine polish. Sometimes a teeny bit of dishsoap.

You use this tumbler and a bunch of little teeny stainless steel pins. they scrub everything off the brass and leave it looking brand new. In my case the bus bars look like brand new shiny copper.






stainless steel pins.


it's a great system, with the only drawback being the brass is polished in water, so you have to dry them out. You can air dry them, some pop them in the oven for a bit on low, and several people make brass dryers.

for the bus bars I just put them on a towel and dried them all off thoroughly. I sprayed them down with WD-40 to displace any water, then wiped them as clean and dry as possible with blue paper towels. They look literally brand new.

 

Just went and ran another test, this is them after maybe 20 minutes in the wet tumbler.

You are right, you probably don't need the pins, the probably clean themselves. But the pins are a PITA to get out of the tumbler, and the advantage of the teeny pins is they actually go through the holes, so they get the inside of the holes as well as the surface. In brass they'll actually clean out the primer pockets. So they do a great job here.



The rest of the bar. I could have gone longer and got every trace but this seemed good enough. If I get this working I'll order nickel plated ones

 

I think I found it. I had originally watched this video, go to 3:42

I had checked every cell resistance to ground. All of them showed infinite resistance, so no leak.

So I assumed they were all fine.

But based on what ChapmanF said, I decided to check with the Megger. The guy in the earlier video tested that way too.

So I checked each side of the split battery. The long side of the pack, farthest from the ECU, showed voltage jumping around and low resistance




So I pulled the bus bar and tested each cell. Cell 12-13 was low resistance and jumping around a bunch.

Every other block showed infinite resistance/no current just like this



I separated 12/13 and 13 shows low resistance. Every other cell showed infinite/4000Mohm resistance.

So I think cell 13 is hosed. Ironically, my lucky number.




Interestingly, my ohmmeter still shows no current from pin to battery case like I was expecting based on the YouTube video at the beginning of this post. This makes me nervous and I'm worried there's another issue somewhere since it shows no leakage to ground with the ohmmeter but shows leakage with the megohmmeter. Weird. But also, I'm dumb and there's probably something obvious I'm missing, like maybe 7.5v isn't enough to push electricity through the breach, but the higher voltage of the tester or battery under load is.

In use, your can reset the codes by unplugging the 12v battery and drive the car and it will go from 10 seconds to several minutes before the code will set again, so that seems to line up with a small leak that only happens under some load, and not when the battery is at rest.

I literally have no idea




Also every cell including 13 show 7.76-7.78v.
Which is good I guess.



I have a quad port battery balancer on the way. I'll cycle the cells and balance them and reinstall a new one on 13.

I still want to test this with ECU plugged into the voltage tracking wires, but I suspect the ECU is ok, and it's this cell.

(Crossed fingers)

I'm going to order 1 or 2 cells, plug them in and put it back in and see if we're fixed

 

I'll order some right now, the one I was looking at on Amazon is showing a delivery date of aug8th to 25th lol. That's not gonna work.

I'll get one from him now