No heat

4500 is a bit extreme. At least the tech was being honest in believing your husband could take on this project. Going forward, it might be time to use a different dealer for any future work or second opinions. Maybe that mechanic would take on jobs outside of work.

Here is the workup for DTC P1121 : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Prius%20Service%20Manuals%202004/%E4%BF%AE%E7%90%86%E6%89%8B%E5%86%8C/04pruisr/05/2054m/cip1121a.pdf

Did you use OEM replacement parts from the dealership, or were the parts procured elsewhere?

Many DIY enthusiasts will use a "mini-vci" cable ($20) and a copy of techstream (same software the dealer technicians use) on a windows device to diagnose/test/repair. How are you retrieving the OBD2 codes (DTCs) currently?

 

I would suspect the coolant control valve replacement did not go well. Bad aftermarket part or something involved with its repair. Based on that code.

P1121 - Coolant Control Valve Replacement (with pics) | PriusChat

 

who did all the work on the car? Maybe you should check the coolant level again, make sure it's full at the radiator

 

if your husband is a mechanic, have him replace the coolant valve again if he didn't use a brand new OEM Toyota part. Shouldn't take him long

 

Knowing that you currently aren't working with a $20 mini-vci cable and a copy of techstream to test and diagnose the issue, you can still go step-by-step through the above workup for DTC P1121 (linked again here : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Prius%20Service%20Manuals%202004/%E4%BF%AE%E7%90%86%E6%89%8B%E5%86%8C/04pruisr/05/2054m/cip1121a.pdf ), just skip the steps that require "the hand-held tester" (now replaced with techstream).

Aftermarket control valves (and inverter coolant pumps) have been known to fail in short periods of time, confirm yours is working. If the valve was purchased at a local auto parts chain, it most likely has a lifetime warranty.

If you had a mini-vci cable and techstream you could read the freeze frame data which would tell you the conditions that were met to throw DTC P1121. It could also tell you the temperature of the coolant, and actuate the control valve into all three positions.

The manual calls for SLLC (super long life coolant), was an off brand of coolant or a stop leak product introduced into the system?

 

Your link shows up as unsafe on my system

 

Don't know what to say, except those share.qclt.com links have been known to be safe on this forum for some years now.

You could allow an 'unsecure connection' by giving the website "temporary permission", but only if the browser gives you such control.

Another option would be to find the needed workup over here : Service Manuals - Google Drive

 

It's generally ok to view materials that are on an "outdated security configuration" site, as long as you are not planning to enter any personal or financial information there, and you're not concerned about whether eavesdroppers might be able to know what you viewed.