which code reader or scanner

I think the best tool for your requirements is the Mini VCI with Techstream software £23 on Ebay. This gives near dealer level of diagnostics at a very cheap price. It can be made to run on Windows 8.1 using XP virtual machine,or by following instructions posted by "3prongpaul".
I use an ancient IBM laptop with XP loaded bought for £20, "rather than risk damaging my house machine loaded with Windows 7" and gets over the minor difficulties of getting the program to run on W 7/8.
For purely monitoring purposes I use an ELM327 (blue tooth version) and Priidash (free). This gives a dashboard readout of just about every perrameter available, and records HV battery module voltages and other information to a file.

John (Britprius)

 

I started with the ELM 327, but wanted the ability to bleed the brakes to change the fluid among other things.
Then one day I was in Birmingham picking up a HID kit from an Ebay advertiser and spotted the mini VCI on sale there. So I bought one. Very pleased with it, the last job I did with it a few days ago was to set the AC compressor not to come on automatically when demisting the windscreen, "something the dealer said could not be done".
This works on most Toyota's and will also work on most cars for emission faults that have the standard OBD connector. With adapter connectors it will work on BMW and Mercedes.

John.

 

The ELM 327 is designed to be an OBD reader engine for emissions DTC's. There is an international agreement on the standards for these codes and the methods of delivering them for engines, but not transmissions and other items. OP "2009Prius" along with others developed a program to be able to use the ELM to display virtually all the information available at the OBD port on the gen2 Prius "Priidash".
The Mini VCI is a Chinese clone of a more expensive device called a Mongoose. This device with Toyota's Techstream software is what dealers use for reading codes, fault finding, and carrying out service tasks to the range of Toyota cars, covering all aspects not just the engine and emissions. This means it is capable of almost anything that the dealer can do. The dealers in the UK will typically charge £80 to read any trouble codes, more than 3 times the price of buying a Mini VCI.

John (Britprius)

 

Scangauge is good for realtime dash monitoring of upto 4 different parameters in the genII, example: I use btv,mpg,rpm,soc.. as far as reading any DTC's it will only read eng ecu standard codes not the hybrid stuff. For that I've been using autoenginuity scantool & dongle and software, been using that since genI days and now the genII with updated toyota enhanced interface it also works great for anything. I use it on a 1.2ghz laptop running winXP. Sure wish it would work in linux but that's a whole nother can of worms..Anyway already got the toyota enhanced interface and software running then to add another family like FORD, just buy that enhanced interface and they give the key to unlock it. The software contains all NA/EU you merely unlock the different interfaces you purchased. I now have 3 Toyota, Chevy and Ford including the diesels. Handy but must have laptop and pay 475+ for software but once u have it, very easy to add on and superior diagnostics capabilities and data recording. For instance I can record all hv battery module voltages and then played them back later on a spreadsheet chart, or how about mg1 current mg2 current and mg1temp and mg2 temp etc etc.. nice