Weird stuff happening? MPGs dropping? Test The Battery

Third gen was the first with any form of EGR.

 

Thank you for replying. Battery is replaced and of course all codes are off after being disconnected. Only 20 min drive home so time will tell. 2 of the other codes were for inverter coolant pump and ECM/PCM pn (? not too legible for 2nd letter I think inverter pump isn't working. I'm going to recheck today for movement in the reservoir. Looking for reputable mechanic.
Wish I hadn't just had surgery I would attempt myself. I love to work on my car. Fixed my cruise control switch arm. Prius Chat is the best!

 

Mendel I forgot to enter that my Prius is Gen 2 it is an 07 with 181000 plus miles. This is the first time other than usual maitenance battery, brakes X 2, wipers, bulbs and my knee breaking the cruise arm ( still don't know how I did that) that I have had codes. Dealer replaced pump, dash and computer module, steering shafted pedal for carpet issue before with recall. So needless to say I love this car and it has been supremely dependable.
Thanks again!

 

After replacing the 12 Volt battery there are no codes but there is no movement in the Inverter Coolant Reservoir. I am going to use Toyota parts because I can't work on my car now and was referred by the garage that does my brakes etc. I learned on Chat that the Inverter water (coolant) pump is the likely culprit.
I am having the coolant drained and replaced because Toyota has never done it when in for maintenance.
Because My car has almost 200,000 miles I am wondering if I should replace the other coolant system components like Water Valve etc?

 

It would be prudent to replace the engine water pump, with those miles. There's an Aisin pump that's basically identical as far as I know; they make the Toyota branded pump as well??

 

Thank you so much for that information. It validates my thought. Much appreciated!