Gen 2 Prius Code P1151 can't seem to fix

Hello, I got into an accident and had my CHS replaced. My mechanic used a Used CHS to replace my dented one. I had the P1151 code pop up shortly after and he kept draining the coolant system total of 2 times over a month saying air most likely in there. I am not sure if he used Techstream to manually run the pump since i recently found out about it. The code went away and would only come back maybe once every 2 weeks for a day or 2..then dissapear I assumed an air bubble in system causing this issue.

Now the code issue is constant, I took it to a new mechanic that specializes in hybrids since my schedule conflicts with my first mechanic. They diagnosed that my CHS pump was bad since it was loud and grindy sounding when it ran, they replaced the pump. Few days later, P1151 comes back. I take it back to them, they say they misdiagnose and replaced the Coolant control valve (for free), they said a couple of the hoses to the CHS was cold after bleeding and running the car to check for air and that that part wasn't working properly since the hoses should be warm.

Here we are today, Code just came back up today, 3 days after getting the Coolant control valve replaced. I am not sure if they used tech stream, they said they used the Code scanner which has a program similar to tech stream??

I bought a multimeter. Should I add a funnel to my cold radiator spout and fill up a couple inches of coolant, manually jump the CHS pump relay to check for air bubbles my own self?

Or what other components could be bad in the replaced used CHS?is there maybe like a bad sensor or something or temp gauge? I cant figure this out and I rather not buy a brand new CHS after replacing with that used part a few months ago

They said they felt the tank and it was pretty warm so it was storing the coolant in the tank and the tank seems to be working fine.

Sorry for the long post.