I can share with you my own experience that is contrarian to what was already said here by others. At the end you are free to choose option that fits you better.
I was in the same situation before that you are right now - I had very unimpressive grades and was really afraid that because of that I will be rejected instantly by all top consulting companies. I decided not to mention my grades in my CV and only send them later on after being asked to do so. My plan was based on assumption that it is best to make a good first impression, I was really scared that if a recruiter will see my grades my application will go right away to the rejected pile and he or she will not even bother to read my cover letter. Despite my grades I strongly believed I should still get a chance inbthis industry.
People have weaker grades from many different reasons and we can not put all to one basket. For many it is just simple laziness or lack of motivation, for me it was the need to take care of my very sick parent and to work night shifts during my studies just to make the ends meet. I assumed that if interviewers hear my story they may conclude that I have the qualities they are looking for. At the end my approach turned out succesful for me - I got invitations for interviews and finally landed my dream job in consulting, despite many obstacles and odds being not in my favor. Of course there are much more factors that matters - how well your whole CV is constructed, is you cover letter written in an interesting way that will convince recruiters you are the kind of person they are looking for and so on and so forth.
I would like to also reassure people who due to low grades doubt their chances of getting into consulting and may even not try applying - dont't go that way! If you will put a lot of effort into your application and prepare well to interviews anything can happen!
Hope this story helps.