I've had a little play with the clone obdii scanner thing,
i have a vauxhall (opel/GM/Holden) meriva B, and originally had a fault where the engine was going into low power mode,
I bought an "op-com" which is an opel/vauxhall specific devise, the real ones are about 800 euro's, but clone ones are available from 10 pounds upwards on ebay (avoid the ones claiming firmware/software versions over 1.7, they are faked to make you think they are newest ones, the absolutel latest op-com clone is firmware V1.71, and software V160115a)
i went for a HQ clone from someone on a vauxhall forum who provided help setting it up if needed etc.
This devise plugs into the obdii port and the usb port of a laptop running the op-com software, and allows you to do quite a lot of things a dealer level code scanner will do,
It diagnosed my fault... variable vane sensor on the turbo out of calibration, it was the variable vane lever seized... i free'd it off and it's worked fine ever since... the dealer cure for that fault code is to fit a new turbo assembly, as the vane position sensor is not available separately!!!
When i was getting high EGR readings and low DPF back pressure readings reported by the op-com, this turned out to be a hole in the DPF sample pipe, a 100 pound part... fixed with some 8mm fuel pipe for pennys, a common fix.
Then i got into adding parts from higher spec cars to mine, and the op-com was struggeling to do what i wanted,
so i bought a clone Tech2 unit from china, this is a clone of the unit the main dealers use on my car (the astra's use an MDI.. but my car is weird it kept with the Tech2 until 2014 model year, whereas astras and corsas were using MDI's since about 2009)
The clone Tech2 cost me £280, i bought it with a credit card via paypal, but have had no issues with it, worked straight out the box, and i have since added quite a few items that would have needed trips to the main dealer to have them enabled (But, vauxhall are getting arsey and refusing to do this nowadays, saying owners are not to take their car out of delivered spec!!)
I can access every single part on my car now, alter things, add new parts, divorce old parts if needed, run all the tuning and calibration routines etc,
overkill for most people i guess, but that's the kind of person i am,