squealing pump, new warning lights, otherwise runs great

I've had my '06 about three years and am the second owner. It's at 246k. I love it, and aside from replacing the hybrid battery a year ago after leaving it idle while I was away for a month, have had no problem.

...Except what happened yesterday and the semi-intermittent (doesn't quite always happen) squealing/screeching fan noise on startup and shutdown that began a few weeks after replacing the battery. Driver's side, engine area.

[Tl;dr -- There's a summary of details at the ** below]

But finances were tight, and the car otherwise ran well, and my search of PC at the time assured me that in the absence of warning lights, I didn't need to worry right away.

Sooo, I'd planned to finally get it looked at next month, and so of course, yesterday, on the freeway, the red master warning light and the CEL came on, as well as the HV symbol on the mfd, and the car popped out of cruise control. Otherwise, all functioned fine. All lights, brakes, acceleration and control ok. I was only 2 mi from home.

This morning I started the car, and the same warning lights came on, but still drove fine, and no temp warning light.

I bought a code reader at Napa Auto, but haven't opened it based on comments here that lead me to believe it wouldn't be as useful as other brands.

***Here's a list of what I think are relevant details that I do have--based on my pc searching so far (please be patient, I'm a relative car novice!)

--Fan, driver's side, engine area, sqealed at most startup and shut down for about a year. Otherwise drove great.
--Yesterday, while driving, cruise control shut off and MWL, CEL amd HV warnings came on.
--I didn't try to turn on Cruise control again.
--MPG has been great: over 48mpg the last several tanks
--MWL and CEL stay on, but when I went to Napa Auto, the HV went away during the ~3mi drive. Came back on at restart.
--The hybrid battery seems normal, charging and holding a charge
--The self diagnostic screen showed the battery at 12v on Ready
--The inverter coolant level was slightly below Low, but the radiatior and other reservoir were full. Topping the inverter cooler reservior didn't change anything.
--I never saw a pattern to when the fan wouldn't squeal--not outside temp, drive time, or whether the a/c or heater had been in use.

I'm wondering
1) if I got a better code reader, whether I might get enough info to semi-reliably determine it was, say, the inverter cooler pump, or the 12v battery, and replace that and save myself expensive Bay Area labor, and

2) if it's safe to drive 20mi to a good Prius shop (or to get my tools from storage)

I'm good with following directions, and have replaced fans and multiple other parts on my vehicles in the past.

Thanks in advance for your insight!

 

I didn't even realize I'd switched terms! And the whole year I've been listening to it, I never thought of it as a fan!

Thanks for your feedback. I spent many lockdown hours yesterday poring over pc to try to winnow down the possibilities (symptoms/series of events never exactly matched the combinations others posted).

While I was waiting for my post to get approved by the moderator, I came to that conclusion, or at least ruled out the 12v battery, based on a test someone had posted--but their instructions were to look for the movement in IG-ON mode. May have been my by-then swimming eyes, but may have been a brain fart on their part like me typing "fan" and pump interchangeably, as I remember the two "tests" to determine battery prob vs pump were in IG-ON mode. Will re-"test" in the morning to confirm the dx.