Just going through this with my 15” MacBookPro9,1. D key has been very intermittently flaky for awhile. Hold it and sometimes it will start working with no change of pressure and no even slight movement whatsoever. Sometimes nearby letters would do the same thing. Really seemed like a software issue. Would come and go, and be perfect for weeks.
Today it was bad. Did the following:
- Blew out debris with compressed air. There was a lot of it. Did not help.
- Safe Boot to clear cache: did not help
- Removed and reinserted the internal keyboard cable connector at the logic board: did not help
- Tried a different OS user account: did not help
- Tried a clean OS (same version: 10.12 Sierra) run off an external backup drive: did not help
- Tried a different clean OS (High Sierra): not only did that not help, suddenly all of A, S, D, F, G were problematic (coincidence or related to earlier work), with D remaining the worst
Did not do a PRAM zap today, but did one several weeks ago to cure this issue, with no improvement. There may be thermal effects involved, and i do eat at this machine so even though i don’t recall any spills, there may be chemical contamination/degradation from a past event.
It’s become so bad that during the course of typing this message, i’ve had to attach an external keyboard. What is really weird is that sometimes mashing down (multiple simultaneous presses, not high force) other nearby keys (the others which intermittently fail) along with the D key will reactivate them both—interesting key matrix stuff going on there, i’m guessing. For me, it’s a hardware issue: keyboard problem. Sad that there seems to be one factory in China making all the replacement keyboards that everyone sells, and that this replacement allegedly does not have the Apple original build quality and feel (and one report of a dimmer Caps Lock LED).
This is my primary Mac and i’m an author, so i need to go with a fully functional keyboard. I’ll nevertheless attempt to fix the current one for use as a spare once the replacement is in. The point of this answer is the sequence of troubleshooting steps and the eventual conclusion that it’s a keyboard hardware failure.