Strange behaviour

I have a 2002 Prius that has recently started acting really weird. This started a few months back when it was still very cold here (around 30F), but it always did this when it was at normal operating temp. While driving around town, the car would suddenly become very sluggish and the engine didn't want to rev much at all. According to the display, the hybrid battery was pretty low (about 1/4 full). This battery was replaced in Jan 2021 from a company that was highly recommended (Micro-something I think. I first heard about it on a ChrisFix video). After pulling over and allowing the battery to charge up a bit, the car started acting normal again. Yesterday on the freeway, I had the cruise ctrl on going uphill, the cruise ctrl disengaged (I had both feet on the floor, so I know it wasn't me), and when I pushed the accelerator, it was again very sluggish and didn't want to rev much. The hybrid battery showed about 1/4 full again. I pulled over, let the battery recharge and everything was good. I hadn't changed the spark plugs since 2018, so I did those today.

Now a new symptom comes up. I took it out for quick test drive to make sure everything is good. I did a hard acceleration up to about 50 mph and took my foot off the gas. The hybrid battery was about half full and I was almost home, so I shifted into the B mode to let it charge up a bit. It decelerated normally for a bit, and sounded normal. But then, with my foot off the gas, it stopped braking (I was still coasting, but no braking sensation) and the whine you hear during regen braking went away. The display showed that power was going FROM the hybrid battery to the the inverter, and FROM the inverter to the wheels! This went on for maybe 3 seconds and then it went back to braking.

The only other simple solution I can think of is replacing the 12v battery. It's not terribly old. I put it on a smart charger if the car goes more than 3 or 4 days without driving it. But money is extremely tight right now, so I'd rather not replace it if it's not the issue. The not-so-simple solution I'm DREADING is the inverter may be going bad. Any ideas?

-Rob

 

Ah, I did forget to include that there were no trouble lights and no DTC's read with my Blue Driver. It completely slipped my mind about the 12v load test! Thank you Bisco!

The inverter pump certainly does make sense. It failed and had to be replaced when my dad owned this car. I think that was about 2008ish that he replaced that. I'm usually pretty good at keeping an eye on the levels, but I'm definitely starting to slip these days. I can't believe I'm saying this, but I wish the problem lasted maybe a few minutes instead of a few seconds so I could hunt for more clues.