2005 Prius Engine Revs, Battery at 1 Bar, and Low MPG on Highway

BACKGROUND:
I've had this Prius for about 2 years now, bought it used from a guy who was I believe the 3rd owner of the car. The first owner got in a front/rear end crash and it was sent to a scrap yard as totaled, 2nd owner bought it and frankensteined the car back into working order. It has a 2008 EV battery in it, and I can't vouch for much else except the parts I replaced which are basically all of the pumps, plugs, and belts a year ago. It was 225,000 miles when I bought it, I'm 251,000 miles now, and yes I know that's just begging for problems, but...

None of the issues I'm experiencing occurred until about a month ago when I accidentally left the dome light on for 2 days on a weekend when I wasn't using the car. Sunday night of that weekend, I went to start the car and it was dead. I only happened to notice the barely dim dome light still on, which is how I knew what happened. I took the battery to Autozone to charge it, but they're dumb (I've never had success with them charging any battery ever. I don't know why I still take them there) and ultimately I got the battery home still dead. So, I hooked up my wife's 2012 Prius to it and jumped it then let it run in Maintenance Mode for a bit to charge the battery. It had worked for the next 3 weeks as far as starting the car and all that, but since charging the battery back up I've been having all sorts of weird issues.

As of last week, I assumed maybe it was the battery still being weird, so I went to Toyota and bought a new OEM battery, but the issues persist...

I have no error codes after putting in the new battery. I've cleared the existing codes relating to the battery replacement and no new ones generated since last week. I also replaced the coils and plugs again last night, still no bueno.


THE PROBLEMS:

The thing is that its not super consistent...none of these problems are. They are frequent (daily), but sometimes the car just drives as expected, sometimes I only get 1 problem, sometimes multiple.

1. The main problem I noticed within 2 days of driving post-battery recharge is that on the highway, the car revs the engine really high when I slow ~5 mph to match traffic slowing, and then re-accelerate again back to normal speed. It sounds like a really low downshift in a normal tranny.

2. After about a week, I started to notice the EV battery never goes over 1 bar once I accelerate from an on-ramp and merge into traffic. I'm a big user of cruise control, so unless I have to slow to match traffic, I usually just cruise. But now that I'm paying more attention to the way it drives, I'm also hearing it rev on inclines as well (not just steep ones). The display will show it as charging then flicking back and forth but the charge never goes above 1 bar unless I'm on a downhill for a bit and then I'm lucky to get 2 bars, yet I'm not seeing any benefit to it still when that does happen.

3. The third thing I've been having an issue with is when accelerating from stop, there seems to be a hesitation to the engine to just GO when I need to accelerate quickly. I'll floor it and it will accelerate, but very slowly for the first 5-10 seconds then it will get the speed burst I was expecting. The engine is running (I know because it has had a pronounced clicking noise for the past 6 months) and the EV has 4+ bars usually, but I get no thrust, just a meander.

Ultimately, my MPG isn't HORRIBLE, but it's not as good as it used to be when I first got the car. I would say it used to be in the range of 36 mpg, and I used to be able to drive to work using 1 bar of fuel, and back using 1 bar, 5 days a week means I fill up every Fri or Sat after work. Now I find myself filling up Thur night so I'm definitely seeing a loss in MPG to some degree.

I'm not against the idea of a new engine, or replacing multiple cells in the EV, or replacing the transmission(?). I knew when I bought it, one of those things was going to go kaput eventually. I just want to nail down the issue if it's fixable.

Here's a video I made today. If you skip to 2:50 mark you can hear the random rev of the engine. I apologize for the vertical video but it was the only way to drive and get the info. I mounted my phone just under the display.

 

I don't know about that. I didn't hook up an odb or anything. I just assumed the car would throw an error in the system check screen or red triangle or something. Should I just go to a Toyota shop to see what's up instead of trying to guess?

 

Any recommendations on code readers that read all codes so I can be sure? Just a standard ODB2 or should I look at something else or take it to a shop? I'm able to DIY a little bit but I'm no mechanic. I've seen some bluetooth ODB plug ins for cheap with Torque. How deep does that go? Enough to tell me "hey dummy, your battery is the problem"? Techstream and the VCI look a bit complicated (not so much the setup, but figuring out the codes and what it all means).

 

The new 12v was fresh...like really fresh. I believe when I bought it, it was 1 month old I think. I don't think it's the 12v. It's getting proper voltage. So, I can rule out the 12v.

What I'm wondering is if there's something between the hybrid battery and the "electric engine" that could maybe be causing the drain, or lack of ability to charge from the engine at high speeds? Because from my understanding, the engine should be charging the battery when running, and if it's exclusively running or the battery is so low it can't even help, you'd think whatever controls the charging between the braking/engine (some kind of alternator?) would charge it up to an acceptable level before trying to use it again. What makes me have any doubt about it being the hybrid battery is the fact that it functions perfectly at speeds 50 and under, unless I floor it. For whatever reason, it can't support a fast drain properly, then recover at high speeds...but at lower speeds I can floor it until it drains, and recover near full battery within minutes.

Watching my wife's 2012 Prius on highways, that's sort of the behavior I see. I get that's a newer gen, but I've never seen it get below 2 bars basically ever.

 

Ok, so I have a weird new update:

As of yesterday, it started reporting false battery charge information. I turned the car off when I got to work and I know for sure there were 2-3 bars left when I turned the car off. When I came back out to leave work, I turned the car on and it said it had 6 bars. They almost immediately depleted once I accelerated from the red light just outside of the parking lot. It was doing the 1-bar thing on the highway, and I stopped on the way home to get something and about 20 minutes later, I started the car up again and it was reporting near full again even though when I parked, it was low.

It did it again today as well. As a test, I floored it leaving work with the 6 bars and the car wouldn't even accelerate. If I barely pushed the pedal about an inch, it worked just fine and had good power behind it. Once I was on the highway, with 2 bars, I floored it again to see what would happen and it gave full juice.

Is there some kind of computer controller board or software that is in the 2005 Prius that controls the battery usage/charging and capacity reporting that could be out of whack and causing all of these issues rather than a failing battery??

 

So some Googling found me that there is indeed a Hybrid Control Unit just outside of the battery that apparently controls charging and discharging of the cells. I'm starting to wonder if that's what has gone bad. From what I'm reading, that thing also is responsible for reporting the health of cells, etc. If it has gone wonky. I'm curious if it doesn't know what the hell is going on with anything related to the hybrid battery status. That may explain why its allowing the "overheating" of the battery and producing that epoxy smell? I wonder if the 12v dying caused some damage to the controller.

 

Here's my Techstream results:

 

Weird thing is all my cells are always at a matching voltage, even when they're high or low.

I took it to Toyota and paid for an inspection and they claim 99% sure its the HV battery. I'm still not sure I trust that assessment. I also don't think I want to spend $2100 on a new OEM because they told me it only has a 2 yr 30k miles warranty which is garbage. I'm thinking I might take the risk with Green Bean since at least they have a 5 yr warranty. I'd like to milk this car at least for a few more years since it only cost me $2000 in the first place, and buying another used car is basically the same price as a Green Bean and at least I know this car's only existing issues are the battery and engine knocking versus buying another used Prius with god knows what's wrong.