Prius stalls after 8 seconds

Aloha! Im a brand new new member so allow me to introduce myself,
I am Optimus Prius.

So heres the story-
I bought an 04 prius with the intentions of fixing and driving it to see what all the hype is about . I bought it cheap and knew it was broken.

The original symptoms were basically a no start, the car was just switched to a new yellowtop optima battery and wouldn't turn on anything except the dash display.

So I got The car home ( I f**kin towed it.. i know... dangit.. its my first prius It has a tow hook and it was only a 10 mile drive... I Didn't know. Now I do lol ) and did some research where I saw DO NOT TOW so I learned my lesson on that quickly but i figured it still never even tried to start so i wanted to figure out why .

So i did a system reset, with holding the start button down and i have made sure both of the batteries were reading properly and traced voltage to try and figure out what was going on. After a day of google and testing I ordered a new HV ecu , plugged it in , hooked everything back up as far as the 12v and the main service disconnect and the car now starts the engine and ramps up for about 5-8 seconds then abruptly stops and dies. I have 0 throttle response and the car won't move durring the time It is on although you can see the car physically try to move, it just cant. The dash lights have been very intermittent, sometimes on, sometimes off with the gas gauge reading either 0 or full. I have a code scanner, the code is P0A9E saying it's the battery temperature sensor. And thats the only code coming up with my check engine light.

So, the car always has had the red triangle of death on since I've owned it the car has a full tank of fuel, has been reset, has a good charged 12v battery, I have cleaned the fans for the hybrid battery.
The hybrid battery is not charged ( only showing 1 bar ) but have checked voltages on each module , replaced 6 modules and now all are reading 7.2 or better.
The car now starts the gas motor ( with the new hv ecu) but again only runs for 5-8 seconds, then dies.

After further research I'm thinking its either

A. The inverter
B. The transaxle

Does anyone have any suggestions on how to test either of those or any other overall ideas? I live in the country part of Hawaii and there's hardly no one with knowledge of this car in the island and there's no dealership here. I appreciate any help !
Thank you!

 

I believe the gas engine starts, i can feel exhaust coming from the tailpipe and it sounds like the motor is running but again if I press the gas pedal, i have no throttle responce after startup for the 5-8 seconds untill it dies .

I know the inverter is driven by the gas motor to charge the hv battery and The hv battery needs to be charged, so that's why I'm thinking it's the inverter not able to send power back to the hv system. It " starts" then seems to almost slowly ramp up Rpm untill it dies.

I am fairly educated and mechanical and have a decent base knowledge of most vehicles and it really seems like The gas motor is on and doesn't make any odd sounds.

 

How can I test the injectors?

 

Ok now it did throw a fuel code one time, saying the tank was empty although it was a full tank. Could it be that my fuel pump/ tank assembly is inop?

 

Hmm. Very interesting. Thank you very much for your help! I will do some fuel system diagnosis tomorrow and see what I can track down and post my findings. That 9v battery tip in that other thread is gold.