[thstone]

The mechanic is doing the best that he can and is probably being honest, but the bottom line is that he doesn't know Boxster's very well.

A check engine light and its associated failure code only describe what general subsystem is out of tolerance or may have failed. It does not tell the mechanic exactly what part to replace. In other words, do not confuse a CEL or code with a true diagnostic test.

It is pretty common for non-expert mechanics and backyard DIY'ers (like myself!!) to replace several parts in order to solve a single CEL. This is often called "throwing parts at the problem until its fixed".

I often do this on my own and accept it because it is often still cheaper for me to replace 2-3 parts rather than pay the labor cost for a proper diagnostic and part markup that a shop will charge.

However, most customers won't accept this approach from a professional mechanic because the reason you're paying the high labor cost is to get someone who should know how to perform a proper diagnostic to determine exactly which part failed and is causing the CEL.

With all of that being said, I don't think that you're mechanic is cheating you; but you would be better served by using an experienced Porsche mechanic.