2006 Prius Codes C1242 P0304 Red Triangle of Death

First post on here but have been coming here since I bought a used (one owner) 2006 Prius a few years back with ~ 125k miles on it. Absolutely zero problems with it until last week. I was driving home from work on the freeway and all the sudden the check engine light came on on the dash and the car started driving very sluggish. I exited the freeway after about 2 miles and went to the local parts store for a scan. Scan codes via OBD scanner were for P0304 (misfire cylinder 4) and C1242 (open circuit ui IG2 Circuit). I managed to limp a few more miles home and pulled the plugs which i had just installed maybe a year ago. Iridium plugs. The darn tips were completed gone/melted (see attached photo)! I checked the coolant and it was (last week) near the neck and quite red - today it was below the neck but i could still see it. Overflow canister was near empty. Checked oil on dipstick. didn't see anything to lead me to believe there was antifreeze mixed in with it. I pulled the 12v battery and it appeared to check out ok via the dash diagnostic (12.4V with car on accessory mode, dipped to 11.9 and then read 14.3V when i started car. Car had a fairly loud knock sound from engine.

Fast forward to today.I started car in an attempt to pull each coil plug wire to see if engine sounded different. Started with passenger side and soon as I plugged it car immediately died, and now the red triangle on the dash is on and it wont start at all. Pulled 12V to see if any water in both rear quarter panels; both appeared dry. I ordered a Mini VCI kit off amazon today to see if I can diagnose it that way before getting it towed to dealer or local shop that can work on hybrids. Previous owner had main hydrid batter replaced shortly before I bought car and it was a fully new OEM battery installed at dealer. I believe the recalled water pump was also replaced under warranty and the inverter pump fluid was changed (I'll have to check if in the intervter pump was also replaced.

Any/all suggestions for troubleshooting are MUCH appreciated!

Here is a video from last week when car still ran and had the noise when gas engine started.

 

i bought the Denso iridium plugs on ebay so perhaps they were fake...hard to say i supposed. the new iridium are NGK fro a box store. I've never seen anything like those plugs being melted like that. I wonder if its possible they messed up the coils.

I'll have to check the folder with maintenance invoices to see if the 12V was replaced. I have had car for almost 2 years now. Main hybrid battery was replace within a year or two of me purchasing car.

Car currently has about 160k on it. I was running 0w-20 in it since last oil change. Oil level was about 3/4 on the dipstick, although i do have to add oil to it occasionally. I bought a PCV valve and was about to replace that when this happened.

 

Update: pulled battery a few days ago and let it sit. Connected battery today. Not red triangle and not check engine light. Once gas engine started it actually sounded pretty smooth for about 10 seconds, and then it started to get the loud sound again I smelled gas (like the engine was flooded). Perhaps its a bad coil(s) after installing new plugs with that noted strong gas smell?

I just got Techstream and am having some issues connecting with the VMI cable. I'll have to research this a bit more. Car is outside and its well over a 100 degrees now with humidity.

 

It's certainly worth a try. If they are wet, what would that tell me? Not proper combustion?

Is there a way to test the ignition coils in Techstream?

 

I pulled cylinder 4 (closest to driver side) last night and it was a bit wet and smelled like gas. Reinstalled and replaced with a new Denso ignition coil. Car started right up and after about 20 second was idling much smoother! I noticed a high pitch frequency from the engine bay and it appeared to be coming from around the MAF area so I cleaned it and also cleaned the throttle body. Car idles smoother after that, but the high pitch frequency is still there. Anyone have an idea what component could be generating this sound? See video below.

 

Glad I dumped the motor oil tonight! As soon as I removed the pan plug I could tell it was severely diluted with gas. Guessing the gas in the pan came from the cylinder misfire.

Pixel 3 ?