“CHECK HYBRID SYSTEM” and high pitch hum after new timing chain and refilling radiator coolant.

Hey everyone!

So I’ve recently changed the headgasket on my 2010 Prius. Unfortunately while putting it back together my dad and I made the mistake of forgetting to tighten the sprocket bolt on camshaft #2 and the chain broke, sprocket was pretty beat up, and bolt was bent as well as the notch that holds the sprocket in place on the camshaft was broken off. 1 new camshaft, timing chain, sprocket, and bolt later the engine was back together!

Here’s where things start really going wrong:
Before I disassembled the engine to fix the camshaft issue, I dumped out my coolant reservoir to salvage whatever remaining coolant I could (I wasn’t aware yet that there is a drain at the bottom of the radiator ) which, as you may have already guessed, caused a vacuum in my coolant system!!! I didn’t realize this until I put new coolant in the car, and when I tried to start it up heard a loud “POP” followed by white smoke and “Check Hybrid System” after checking all of the hoses I tried one more time and having the same problem realized what I had done.

Flash forward to this morning: I’ve drained the coolant properly, completely filled the car up with coolant, and put it in maintenance mode so that the coolant could cycle through. About three seconds into the motor starting up I get “Check hybrid system” and the motor shuts down. A high pitch hum starts from the bottom left front of the engine near the water pump. I immediately turn the car off and start looking to see if any hoses are still off/any plugs aren’t completely connected and low and behold a hose isn’t attached to the install manifold. I put it back on and try to start the car up to maintenance mode to cycle the coolant- no luck, same warning sign, same high pitched hum.

Does anyone have any ideas of what could be wrong now? Before the chain broke the car started and drove. The only thing that differed from taking apart/putting together the car Between the head gasket and the timing chain has been the way that I drained the coolant.