Who should I tell about switching a group-based course to pass/no credit? First, some background:

I'm currently involved in a course which is based around a major group project.  However, the end of the semester is coming up, and I honestly can't see this project becoming anything other than a massive trainwreck.  (4 weeks to go, and people don't even have basic features working yet)  Therefore, I'm planning on switching this course to pass/no credit, so I'm not killing myself at the end of the semester under the crunch/workload.

At my university, this is possible with just a signature from my academic advisor, so there isn't any need (from an administrative/paperwork perspective) to tell anyone that I did.  However, I'm not sure who should be told from a political perspective.  On the one hand, it might be a good idea to tell my fellow group members about this, but I don't want to add more fuel to the fire of an already failing project (I don't want them to feel like they've been abandoned).  On the other hand, because pass/no credit means that I don't have nearly as much at stake for the project, they should probably know that this course won't be my top priority relative to the others that I am taking this semester.  In addition, I don't believe that the project advisor would get told at any point in this process, unless I inform him of this.  On the one hand, I feel like I shouldn't tell him how little confidence I have in this project (as it's one that he and the department are interested to see the success of), but on the other hand, I think he also deserves to know.

What would be the best way to deal with this situation?
First of all, saving this group project should be your top-priority. This is still in your personal interest since failing projects tend to get people failed in the class entirely. Also: later in life you are going to have to work with other people and things might get very difficult. Turning this around now is valuable experience for later in life when there is really something at stake.
My advice would be to talk to your group members and make a plan to get things going. If the problem is other group members refusing to work or handing in significantly sub-standard work, talk to your professor about it now. 4 Weeks is enough time to get a lot done, that gets a lot harder with 3 or even 2 weeks left.
The issue isn't that you might appear to abandon them. You yourself are now planning to put less work into it than what you yourself think the project needs to succeed. So the problem is that to a degree you are abandoning the project.