Help with codes?

How did you depress the caliper piston exactly?

Toss your generic OBD2 reader in the electronic recycle bin or donate it too Goodwill; reads too few codes and reports incorrect codes for the Prius. Get mini VCI w/ Techstream ($25-$35 Amazon). Easiest to use on an obsolete 32-bit Windows laptop running XP.
You: P0420= freeze frame
TechStream: P0420 = Catalyst System Efficiency Below Threshold Bank 1 (most likley cat converter needs to be replaced)

1) Don't believe everything you read online.
2) Did the source prove he/she followed the Factory Service manual.
3) You did something wrong.
4) Do yourself a favor and get the factory service manual; no more uncertainity.

Read this post to learn to convert CHM to PDF.
Toyota TIS download tips | PriusChat

Toyota TIS (Technical Information System), is a paid subscription, well worth the small cost:
https://techinfo.toyota.com/techInfoPortal/appmanager/t3/ti?_nfpb=true&_pageLabel=ti_home_page&SMENC=ISO-8859-1&SMLOCALE=US-EN&SMAUTHREASON=0&SMAGENTNAME=%24SM%24mT%252bGLraBu9CwUVnZg4mEDzB2kysT90hgbwsWgdZzNOc%253d&TARGET=%24SM%24https%3A%2F%2Ftechinfo.toyota.com%2F

 

I suspect the OP's scan tool was trying to say that the P0420 had freeze-frame data available; the ECM will save a bunch of data like speed, engine temp, throttle position, etc., at the instant the code is set, in case it helps track down a problem.

The point's well taken that the best place to look up what the codes mean is in the Repair Manual, specifically the one for your model and year. Some of the codes do get reused to mean different things between different models, or even different Prius generations. Too broad a google search can just bring up goodness knows what, and send you down blind alleys.

I've seen the posts about the techinfo content being CHM, but I think that's a bit speculative; it might be stored that way on their servers, but you wouldn't know that for sure unless you worked there. Out here in customerland, we just see them get served up as plain HTML and CSS, with images in very standard forms like PNG. The wiring diagrams use a lot of SVG and JavaScript.

But then, that post that says "chm" is really only giving instructions for generically printing web pages to pdf, so it certainly works, whether or not chm has anything to do with it. The resulting pdf files will have dead hyperlinks, though.

-Chap