I'm doing the Bosch diagnostic tech course and really enjoying it. Planning to do the master tech after. But it's the people I meet on the courses that keep me going in between. We call each other for advise and share info sources.

Books i read are hilliers, scannerdanner, Dan Sullivan (electronics for mechanics) and sites like btn turbo and ngk have stuff to read along with mini courses.

One of my favourite though is scanner danner Premium for around £6 a month and he does his 8 week college course through you tube so you are basicaly in the class with him and hear him interacting with his class while working through his book, as well as his case studies.

Hope that helps.