My advise is after you decide which hole to probe, you should put the cap back on and find out what the system on the other side of that hole does.
There are various levels of repairs that should be attempted by an individual. Code interpretation should be handled by the best tech in the shop. Codes are the second step in proper diagnosis. First is verifying the customer complaint. No code is important if the hypothesis of fault will not address the customer complaint. This connection is the heart to good repair diagnostics and is based upon intimate knowledge of the effects of proper and improper function.
Diagnostic insight is aquired through intimate knowledge and years of experience. Using diagnostic insight one takes the codes and developes testing to prove the hypothesis created in ones mind.
Your questions aren't dumb at all. The represent some of the best questions I have seen this week end. I have always said that the most imporatnt thing a technician should know is what he doesn't know.
Bosch Master, ASE Master, L1
33 years MB technician