Multiple issues, I could use some experience and tech savy

Bought a nice looking used 09 Prius. 144K miles. Drove it for one day and the check engine light was on. It needed engine coolant. Also the Mass air flow sensor code produced. Cleaned the sensor, it looked in great shape. Also cleaned the intake housing and filter. They were filthy. Air flow code was cleared but came back the next day. Ten days later the red triangle of death showed along with the 0A80 code. It suggested changing the HV battery. The previous owner mentioned they recently had it replaced and w

The name of the shop. I called them and it was still under warranty. The battery was exchanged. All codes cleared except for the Mass air flow code. Ten days later the red triangle appeared and the car refused to go into gear and the engine refused to stay running even in safe mode. Extra code also presented. SO I decided to tackle what I could. I looked at the additional codes and took to the internet. I figured since I have rebuilt a few motors I had a good shot at fixing the car. Here is what resulted:

1. Replaced inverter coolant pump and sensor, flushed inverter coolant (it looked good).

2. Replaced engine coolant pump.

3. Removed and thoroughly cleaned the throttle body (ugly) and cleaned the intake manifold (also ugly).

4. Replaced the 12v battery after it failed a load test.

5. All parts are Toyota OEM.

6. Since I removed the front end, I polished the headlights and replaces the wiring.

All codes cleared except the 0A80 and 3190. The car still wouldn't go into gear and the engine still wouldn't stay running. It continued to shut off prematurely and the smell of fuel let me know it was loading up in the intake.

TO THE DEALER IT WENT. The dealer blamed the HV battery. They also said it needed a new fuel tank and fuel sending unit (more on that in a minute). They would not do any further work until the battery was replaced (they just happen to sell them). It took five days but the HV battery replacement company went to the dealership and replaced the HV batt. They insist it is not the battery but have been great about everything. The dealership called. It is a technician consultant, not the mechanic. She relayed the car needs a new fuel tank (it is empty but reads two bars, I've asked twice if they have recalibrated it since I swapped the 12v battery while it was down but can't get a straight answer). They insist it still needs a new battery (HV) and ECU. This is the third HV battery since April. The dealer also say it needs a new battery exhaust fan and filter and were quick to point out the battery replacement company didn't do that. They also want to do the spark plugs. The repairs total more than the car is worth. $2500 for just doing everything except a new HV battery.

I have to decide if I should trade it at the dealer, fix it and trade it elsewhere, fix it and keep it (if I am confident it will last). Also, if I fix it what to do myself and/or have the dealer do.

I need some support and guidance. I should also mention I have access to an 07 Prius that has been sitting for a year.

 

Update. I will let you know when this is confirmed but here is the diagnosis and the backstory. The car was towed from the dealer to a specialty shop and sold. I took a negotiated loss, but the car will at least be fixed and not dumped onto someone else. The dealer's total for repairs was basically the value of the car and also incorrect. The HV battery was definitely not the issue but Toyota wouldn't back off of it. That is basically why it was towed somewhere else. I've learned the dealership isn't a place for complex problems. So here is the verdict: The main problem was an intermittent fuel sending unit. I figure the gas mixture was lean at times and caused the engine to not run. We mistook the engine trying to start as actually running. That explains the occasional fuel smell. It explains why the battery kept running down and sending the 0A80 code. It might explain why the Mass Flow Air code P0101 kept popping up. The unburned fuel would track enough to set off the sensor. The car just needs a replacement fuel tank assembly (for those that don't know, the sending unit is inside the tank). There were other codes and the car probably needs a few more smaller fixes, but the car should become drive-able.
Thanks TMR-JWAP for giving the missing piece to the puzzle.

 

I don't think its a cooling issue either, but a good technician would have just tested the fan and maybe cleaned it a little bit. I'm pretty sure the tech didn't go that far. Thanks, read the post below. You gave me some info I hadn't considered and it cracked the case.