Diagnostics tests - what do they show?

[coopma]

Could use advice please. I took my 2004 4Runner in to the Toyota dealership for maintenance. They charged me $250 to run diagnostics for (they say) 2 hours.
1) What does running the diagnostics entail? (plugging in a plug and hitting the enter key on a program?)

2) What all do these check?

3) What all do the results show?

4) Can I get a printout?

5) Pros and Cons?

 

[BlackWorksInc]

Depends on the issue. It could be as simply as me spending 10min to do a health check via the TIS Techstream and both laughing and grumbling for wasting my time as I click the gas cap closed.

Or I can spend hours trying to figure out what your car keeps setting a code for a problem it doesn't exhibit.

Depends on the problem.