H,
Tune boy doesn't really tests but runs a sensors check through Tuneboy Diagnostics. and also gives Error Codes in diagnostics.
When my MIL light went on it showed what faults the ECU (engine) had (P0223, P0505, & P0638) and with a little fussing I manage to get the light off and now all is fine.
Yes, I can imagine at $85 an hour at the shop to get the same answers and versus be able to do the adjustments myself would have cost. Me $0, discounting the initial cost of Tuneboy, shop $$$$ but their learning curve might be higher. I'm still learning.
Cane - I'm glad it is working again. Did CB work on it or did you wash it before going (# 1.)