[mikefocke]

My bet is what he was implying is get the right tools and get the right instructions and do the right tests and interpret them correctly. Instructions come with flow charts and lots of details. Test this this way and if you get these results then do this. For these codes they get complicated.

There are samples here if you search for those codes. Though they may not match your specific engine.

Or pay the person who has all that and the experience ... which is liable to be cheaper than shotgunning parts.