What do these codes mean?

Have you looked at the fuel consumption being reported over the CAN, like with a ScanGauge or something? I'm not familiar with the raw CAN data streams (which is apparently what your codes are from?) and a quick online search of OBD-II PIDs didn't show anything that matched, not that I'm familiar with parsing CAN data. So a product that interprets the data would be handy.

Since you've been working on the older Prius for awhile, I would believe you're familiar with the car's operation, but just in case, you know the electric motor kicks in and out occasionally by slight changes in load (not speed), and this will affect the fuel consumption. I am thinking your gauge is telling you what the car is experiencing.

 

Well then, that's your problem -- you've got network difficulty,
nothing specifically related to fuel consumption. Do you have
the electrical diagrams so you can start tracing signals?
.
_H*

 

I'm not sure of your electronics level, but to check a static line, like power or ground, or one that changes at human speed (you can turn it on or off by hitting a button, for example), a voltmeter is all you need. If it's something that can change quickly (like the communication bus), you'd need an oscilloscope or something similar. You can do a lot with a voltmeter (and an ohmmeter).

Going thru a schematic, finding the wire in question and checking its level can take a lot of time. It also helps to be able to find pin 1 on a chip or connector (usually there's some subtle indication, like a dot or an angled edge or square solder joint). And obviously you don't want to accidentally short something when the power is up, or you could be in worse shape than when you started.

I'm a little confused though. If you don't think the ECU is working, how is the car getting to the point where you can monitor the MPG level? I'll admit I'm no expert on car electronics, but I think it wouldn't get out of the driveway if the ECU is dead.

I think you can get the schematics from John1701a's site: John's Stuff - Toyota Prius and more ... edit ... must be copyrighted, neither he or Hobbit seem to have the schematics online, although I'm sure they both have had access, so I think there must be a non-disclosure agreement you need to sign to download the docs from Toyota. Not sure how a library would work that.