Do you have to have all Honda parts in the car for the car to be diagnosed ?

Honda at memorial told me my car needs to have all OEM parts to properly be diagnosed . They want me to replace my alternator that tested GOOD! Because that’s what they think might be the problem then they can “DIAGNOSTIC PROPERLY”

No at all. Let them diagnose first, tell you what's wrong, and what needs to be done. Then they'll recommend the parts. But they'll do all that

They are ok. But you get better service at gillman honda on bw8 s and 59

No , they can do diagnostic , find what is needed and order it if they do not have it.