Can I correct a mistake that the reviewers didn't spot in a paper that has not been accepted yet? Recently my paper was accepted pending major revisions (i.e., not yet accepted), and while following the reviewers' comments and revising my paper, I realized that both reviewers missed a mistake that I made in a function block diagram. What should I do?


Correct it and let them know in the joined point-by-point response?
Wait until they tell me about it? 
Ask them to double check that diagram?


I'm afraid it may send the wrong message and I'd look disrespectful by showing them that they missed the mistake.
YES.  The responsibility for correctness of the paper is yours not the reviewers’.  The reviewers may help you find errors, but that is secondary to their main function: recommending to the editor whether to publish.