Red Prius 04 With 275K Miles

The 12V Was around 10 Volts

I just about sprayed my drink all over the computer, lol.

Personally, I would fix the obvious first, before I invested a lot of money into anything else.

Get the 12v system sorted out first. Without a good 12v battery/system, you're just peeing in the wind. That may be enough to get the Combo meter working again. Once you're able to start the car, try to force charge the HV battery. Your HV battery probably has some weak modules that self discharged while dormant. They may charge well enough to get the car operational again. Somewhere down the road, weeks, months or years (who knows) you may need to replace the battery.

Just because a Prius sits for a month and a weak module in the HV battery self discharges low enough to trigger the codes doesn't mean the module won't accept a charge and recover enough to get the car working again.

 

I recommend dis-assembling your fan. No matter how delicate a Pick you may have, there are too many crevices inside that housing.

 

Keep in mind, that the copper busbars are sandwiched between the nut seating surface and the base surface of the module threaded stud. VERY rarely does the corrosion spread to that area. Think of it like this...although the outer surface of the nut and copper busbars has corrosion, it's electrical conductivity should be unaffected as long as the copper is clean in the surface contact area. If you turn on a floor lamp, then spray paint the power cord, does the lamp stop working?

 

Then one or both of the modules in Block 1 has a discharged/failed cell inside. If all the other blocks are 14.x volts, they're also very weak. How long has this battery been sitting? I have modules that have been on a shelf for a year and are still 7.5-7.8 volts each.

Any chance that your car has tried to start, but just spun the engine without it actually starting? Do this a couple times, and the battery becomes drained to the kind of voltages you're seeing.

 

ok, let me provide some recent examples. I have about 1300 modules in the shop, and I've been doing a lot of cycling lately to refresh ones that have been idle for many many many months.

The individual modules are rated for 6500mAh when new. Think of it as when they are 100% charged, they have 6500 units of energy inside.
Here's some data from one pack of 28 that finished last weekend.
I always record the initial module voltage and then do a discharge first to document how much energy is remaining in the module.
25 of the modules were 7.63 to 7.73 volts and contained 2500 to 3350 units of energy, even after sitting almost a year.
1 module was 7.31 volts and contained 499
1 module was 7.18 and contained 408
1 module was 7.35 and also contained 408

So now, if you're saying all your other blocks were about 14 volts, then those modules (2 per block) are averaging only ~7 volts each. See where I'm going with this? If that is the case, they're sitting at less than 5% state of charge. That is a big problem.

 

What I'm saying is that it appears to me that your problem isn't that you have a single module failure. It appears to me (if your voltage readings are accurate) that your HV battery has severely depleted itself across ALL modules. The one that's reading 12.x is just a result of the severe depletion, not necessarily due to a module failure.

I've seen this a couple times in Gen 2s that have run out of fuel. The battery depletes itself trying to run the car or trying to restart the engine. After a few attempts, what was once a good strong battery is now a severely depleted battery with all modules very weak and one, two or three modules that are in the 6 volt range. Especially if the 12v battery is disconnected and then reconnected. Then the SOC indication resets to about 60% default value and it tries to start the engine again, resulting in even more depletion, until the battery is effectively useless.

The last time I helped someone with this problem, the battery 100% fully recovered just by recharging the modules. No module swaps were required.

 

Is there a line item on your documentation that shows what current draw was at the time the voltages were taken? A larger current draw will cause voltages to be lower. That may be why they're showing in the 14.x range. If it's a decently large draw, then those voltages could be totally normal, except for block 1, which definitely has at least one module failing.

 

That would be the white square/circle with the negative cable passing through it, near the bottom left corner of the posted image. You can also see it referenced on page 7 in the PDF linked below.

Please use this PDF for safety precations and related DTC workups, like P0AC0, etc. https://attachments.priuschat.com/attachment-files/2020/03/183963_Hybrid_Battery.pdf

 

OK, there can be a big difference between voltage readings on TechStream while the car is live (with battery under load) and voltage readings taken when the battery is removed and under no current load. If you are measuring 14 volts on the blocks while the battery is removed from the car, then post 31 applies. The battery is depleted. This also assumes the voltage readings are accurate.

It is very likely that you don't need to disassemble the battery. If your voltages are accurate, it merely needs charging.