2012 Toyota Prius is alllllmost happy, but...

Howdy y'all, first time poster, although I've definitely read through plenty of y'all's threads before trying to figure out my cars issues. So on that note, I'm gonna go through a whole big long history of fixes/repairs, but I'll also include a cut off for anyone who wants to skip the backstory.

So anywho, I bought a 2012 Toyota Prius back in October last year '24. Had about 140k miles on it when I bought. All was well for about the first three months I had it until it started doing what I would come to learn was generally termed the "Prius death rattle" on startup. Took it to my usual mechanic who advised it needed new spark plugs and ignition coils and wanted I think (been almost a year so I'm not 100% on the numbers anymore) about $1400 to do it. Now prior to this whole odyssey, I've done just about zero car maintenance myself beyond just swapping an engine and cabin air filter and replacing windshield wipers, so yeah, basically nothing. But I heard that price and for some reason my brain said "That's not supposed to be a very difficult repair to do," so I looked it up on YouTube, saw it didn't look that complex, and decided I was gonna give it a try myself. A little under $200 later (ignition coils, spark plugs, and just a couple tools I didn't already have), and the car was running again and the rattle seemed to have gone away.

Until about a month later when it started rattling on startup again. By this point it's about February '25 in case you're trying to keep track of my timeline in your head. So I hop online and start doing some research and find that this issue falls into two camps: The "Anytime a 3rd Generation Prius does that it's the head gasket," camp and the more, "Yeah, the head gaskets do fail, but it's not ALWAYS the head gasket, try these other things first," camp. So on the advice of some of the folks from the second camp, I did a few other things that were preventative or at the very least would eliminate other possibilities before I could confirm that, yup (spoiler alert) it was in fact the head gasket. Pulled out the intake manifold and EGR cooler and completely cleaned out both of those, and replaced the I think it's called PCV valve while I was back there and had that stuff out of the car.

Now the big issue here is that those procedures were a measure of magnitude more in-depth than the spark plugs/ignition coil issue, which meant it took a lot longer because it was more complex, I was learning as I was going, and it seemed like every other step or so I ended up needing another tool I didn't have which meant I had to go order a tool (couldn't drive to get anything most of the time what with the disabled Prius) and then wait for it to arrive. Also drained and replaced the coolant while I was at it. So by the time I finally had the procedure done and put the car back together, I'd made the mistake of not driving the Prius for probably 3 months and had accidentally killed the battery. Whoops.

So I ended up buying a refurbished battery (All I could afford) with at least a 2 year warranty which in theory will cover me until I'm out of school and can make a decent living (assuming I don't flunk out, at which point I'm utterly screwed, but I'll go post that on I do not know dentalchat instead of priuschat). Greentec installs the battery, every thing seems good.

Then a month or so later the death rattle starts back up. I'm keeping an eye on the coolant levels, trying to figure out what the heck is going on, and then one day I pop open the hood and see that the coolant has noticeably dropped, and at that point I know what the issue is. *sigh*

*Backstory ends here.*
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*Well mostly. Obviously I still gotta give you an idea of where the car is at for diagnosis purposes*

So for those of you who didn't feel like reading the whole backstory, here's where the most recent stuff starts happening. I find an independent mechanic who will replace the head gasket for $1800 flat. Not great, but better than the corporate shops who want $3-4k to do it. Head gasket gets replaced, but as soon as he starts it up, now we've got some new issues. Check engine light is on. I pull the code. MDF sensor. Jiggle the connection around (it's done this before) and that's cleared. Awesome. Other big thing is I've got the orange triangle and the CHECK HYBRID SYSTEM warning AND now the AC isn't working, or more accurately, it's blowing, but it's blowing hot. But the car itself is running and I have to make it back home ASAP because the first day of the semester is the next day (It's now late August).

So I drive on home. Car seems to be running fine, but then a few days later I'm at the grocery store and it starts having issues starting. I manage to limp it home, but I see the hybrid battery is no longer charging and is QUICKLY losing all its energy. I barely make it home, but after that I can't get it to start and even if I had, no way in hell am I gonna try to drive it back up to Atlanta from Macon to get to Greentec who, to their credit, honor the warranty on the refurbished battery. So I get it towed back up to Atlanta. They put in a hybrid battery and it apparently immediately failed, so they save they've got a new delivery of batteries coming in a few days. Personal life is utter chaos in the meantime trying to get to school and whatnot, but whatever, I make it work. Driving up the road with my girlfriend to get the car when I get a call from Greentec. They've put in three batteries before they realize there's no flippin way they've got a whole truck full of dead batteries and there's definitely something going on with the car itself. Car starts, car drives, AC is still blowing but hot, and I've now got, and I'm working from memory as I'm not in the car right now, but I've got the P0A80 death of battery warning, and then when I drive for a bit, I also end up with a (again from memory) P0AA6 Ground fault error warning.

Now I live in Macon. Not exactly a small town, but not a big town either. I call all around and can't find a dedicated hybrid mechanic, so I resign myself to going to the dealer. They of course are no help and only try to sell me a new battery. They do however tell me I've got two sub codes, one I can't remember right now but that to my memory is essentially redundant it's a ground fault error type info, but the other one is 614 which leads to the inverter.

*Real end of any and all backstory*
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So here's where I'm at now. The car is running. Mechanically I don't think it's felt this good since I bought it. No more death rattles and the hybrid battery seems happy as well as I'm generally averaging high 40s, low 50s mpg which is GREAT! This is why I bought the dang car!

But I've still got the orange triangle and the CHECK HYBRID SYSTEM warning and my AC is still blowing hot. So that leaves three possible issues. The inverter is failing. The AC compressor is failing. OR perhaps that spiffy little high-capacity fuse with sand in it, that 90982-11050 part inside the inverter is failing. Regardless of which it is, I've watched videos on all three and I'm 99% this is actually back in my wheelhouse, whereas the head gasket, watching videos of that, I thought, "I could probably do that... but not quick enough to not kill another battery."

So here's where I need the advice and guidance of wiser Prius mechanics and afficionados than myself as, again, before January of this year, I'd never once attempted any sort of remotely in-depth car maintenance or repair myself, but now I'm absolutely broke, so I gotta fix this myself.

My thinking is that, given that I've driven several hundred miles at this point, the inverter must be alright. Surely if that thing was close to death, it would've died by now. Also the AC was working fine before the head gasket replacement, no signs that it was failing, just suddenly stopped. Which to me sounds like a shorted fuse. The fuse is in the inverter, and it is connected (electrically) to the compressor, from what I've learned. Electrically, everything else seems good with the car. I know this can set off that P0AA6, the issue is in the inverter, the AC isn't working... I know I've had a few other thoughts/clues that lead me to believe it's that fuse, but I'm forgetting them right now.

Now, I know if I plan to open up that inverter, I gotta take precautions to make sure I don't zap myself. Gotta pull out the orange hybrid battery safety plug in the back. Disconnect the 12v battery. Leave the car for at least 10 minutes so the inverter... I don't remember exactly, something about stored energy.

Then I can actually check that spiffy little fuse 90982-11050. Now beyond visually, how the heck do I check if a fuse is shorted? I've got one of those little electrical testers but it's something I've only used a few times, so I would not say that I am familiar with it. I used it to fix my dryer one time, but I was following along with a video step by step, and I know I've tested some other electrical doo-dads, but testing a fuse in a hybrid vehicle is new for me. I think I've also seen videos of someone using one of those to test the various electrical connections to the inverter?

Any and all guidance, wisdom, information, etc etc is welcome! I need to fix this dang car. Life without a car is very challenging, especially when your stupid (though admittedly mostly likeable) professors decided on your behalf that one day a week your classes are going to take place at the other campus 40 flippin minutes down the road (wanted to put that mostly likeable disclaimer in there in case it turns out any of them are Prius lovers/home mechanics). If you've read all the way here, my god thank you for your patience, lord knows I know I can ramble, and I look forward to your insight and wisdom!