Red Death Triangle, Engine check, VSC, Red Exclamation Mark Car, How bad? Houston

Hi guys, I bought my Prius 2007 a year ago, it had 220,000 miles, now it has around 250,000 miles.
At the beggining I had to replace the 12V battery so I bought a Super Start. Everything worked fine after that, changed the air filter, now the A/C started to fail, I had to refill it, but sometimes it doesn't turn on when I turn on the car, also I had the engine checked with the Oxygen sensors codes to be replaced, but the light disappeared after a while, so I didn't pay attention to that.
Around 3 to 4 months ago, the dashboard didn't turn, so I was not able to see the speedometer while driving, and I couldn't turn it off until I kinda reset it and waited for a while, ( most of the times this happened on rainy days).
Last week while I was driving I had all these lights on: Red death triangle, Engine check, VSC, red exclamation Mark car, and I kinda freaked out, but the car drives fine, although I've been noticing that the car has been getting very low mileage, I used to have around 50mpg with Techtron (exxon injector cleaner) and 48 normally, now I get around 41mpg.
I took it to Autozone and the guy did the check and I had this:
P0A93 Inverter A cooling system performance
C1300 Malfunction in Engine control unit.
Plus the oxygen sensors.

I haven't done the maintenance of the cooling fluid ever, so my guess is that i have to do it and maybe the P0A93 will go, but I don't know about the C1300, maybe by just replacing the sensors?

I am in Houston, is there any good Samaritan, that could give me a hand? maybe a shop, I am willing to assist in the fix if its at home as well and still pay.

 

I just called Toyota, and told me that the car was bought in October 2006, so it will have to be out of my pocket, 120 dlls + taxes to diagnose, plus parts and everything + my organs.

Is there any shop in Houston ?

 

I actually did reset the Red exclamation mark car, and it came back very soon. The coolant tank has some like dry fluid on the edges and the slip. I checked the 12V battery, 12.2 off, 11.8 start, 14.2 ign-on.

 

I just turned on the prius for a while, drove it a little bit( from the street to the garage) I checked the coolant tank and no movement at all, the fluid stays stills, is on low by the way, thats why I think it need to be replaced and everything.

 

What about the oxygen sensors?

 

Yup, I actually did earlier, to verify that the combo meter failure warranty wasn't available anymore, Do you know by chance if there is a way to still get the warranty? you know its 9 years, and they told me I don't qualify because it was bought in 2006, and I think I still should get it, it is 2007, give me a break.

 

So you would say the water pump might be the cause of the oxygen sensors to activate? because honetly the car looks like new from the bottom, and I think they even installed an universal catalytic converter before I bought it, and I heard that those make the oxygen sensors failure to activate. What do you think?

 

I've been getting those codes activating for a while, but then they clear out by their own, I just really want to get my millage up again, You would say that the water pump is just esencial right?