P0C73 code after head gasket replacement

Hi all,

I have just finished replaced the head gasket on my 2010 Prius with 208K and decided to replace inverter coolant while I'm at it.
I now received P0C73 code with check hybrid system on display.. I don't believe my inverter coolant pump is faulty because it was running fine before I replaced the head gasket and replaced inverter coolant..
I plan on taking everything apart later to see if I have disconnected the plug to inverter pump, and at the main time though I would post here with my issue while searching for related info..

Thank you all in advance for any information!



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Not sure, is there a way to check it?
I thought it's a straight forward of drain and fill based on the videos I've seen..
I fill it to full and then top it off couple of times, I then noticed there is no fluid movement inside the inverter reservoir after I saw the warning on screen...

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I have, and coolant level have dropped couple of times. And the amount of coolant I put in seem equivalent to the amount to that had came out...

With Check Hybrid System warning and OBD code P0C73 right after I filled both engine coolant and inverter coolant, I'm now wondering if my inverter coolant pump just so happened died after I changed the fluid or I somehow unplugged the inverter coolant pump when I taken the engine apart for head gasket replacement???
If later, I have no idea where that plug is located...

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I'm hoping to find the necessary steps to check all components and its location, hopefully I'll find the culprit of the issue..

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Thought I would update my findings and solutions to my issue, in case there are others have encountered the same..

So, after I've changed the inverter coolant and torqued the drain plug to 29ft/lb I proceed with refill coolant back to inverter coolant reservoir. After couple of top off the reservoir to full mark, I received P0C73 and Check Hybrid System warning..

I was almost at the point to order a new inverter pump just in case I need a pump replacement since I couldn't find any definite solution, even though I know I didn't do anything to cause the pump to fail and thought I could hear pump noise but I couldn't see fluid movement in reservoir.( Strange )...

This morning after taking a break from it for a week, I decided to check if there might still air in the system and I proceed by squeeze the reservoir return hose with my hand and saw air bubble coming up and after few squeeze I then saw coolant level has dropped down from the full mark... After I top it off, I started Prius and inverter coolant dropped farther but the warning and check engine light both went off, I topped off the coolant and then took it for a 5 miles drive up and down few hills.
Now I'm happy to report all is good and engine is running smoothly after the head gasket replacement!

So, I couldn't see any fluid movement in inverter reservoir until Prius is actually in "ready" mode. Strange I know, and this may have caused for me to believe the coolant system was full after topped off a couple of times and therefore activated the P0C73 code...


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