Certain keyboard keys not working.

There is a possibility of water damage, more likely when some of the keys are not working as that’s how they go bad. Generally if there are no apparent problems other than the keys not working it should be just the keyboard that needs to be replaced.

I would check the board just in case of liquid damage, generally you’ll see it at the top of the board (check other side too before doing uppercase replacement).

MacBook Pro 15" Unibody Late 2011 Logic Board Replacement

The keys C, D, E & 3 are on the same line so it’s clear the keyboard, its cable and/or its connection to the logic board. have a bad line connection.

Think it this way… The keyboard works on the X & Y set of lines, so X is the horizontal run and Y is the vertical run.

You’ll need to inspect the logic board for corrosion at the keyboard connector as well as check the ribbon cable for damage.

Using a meter you could also trace out the wiring within the ribbon cable between the keyboard to the logic board. Frankly, I would just replace the cable if i felt that was the issue. Unless someone has been poking around inside that would be the least likely issue.

Corrosion and liquid spills are the more likely. Which focuses us on the logic board and the keyboard its self.

My left shift key and the left option key doesn’t work. I took the motherboard and swapped it with a keyboard that works in another Mac, and the problem was still there. So it cannot be the ribbon cable or the keyboard itself. If it is on the board, how can I troubleshoot?