Internal keyboard, key malfunctions.

First you want to try and reset the SMC and NVRAM on the Mac.

Resetting the NVRAM:

• Press and hold Command, Option, P and R together.
• Hold the buttons until the Mac reboots.

SMC reset:

• Shut down the computer.
• Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
• On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
• Release all the keys and the power button at the same time. Press the power button on the computer to turn it back on.
  • Note: The LED on the MagSafe power adapter may change states or temporarily turn off when you reset the SMC.

If this does not work, try cleaning the keyboard with canned air. Sometimes this helps, but not very often. Removing the keys can help, but it is not a requirement*. If you have long nails or a pry tool, this will do the trick to get the keys off of the keyboard on the Mac. You want to remember EXACTLY HOW you took off just in case the scissor hinge comes loose in the process as well.

*Butterfly keyboard warning: DO NOT DO THIS! You will ruin the keyboard and will require a upper case replacement. This did not account for a “feature” added in 2016 and dropped in 2019 because I don’t have a time machine to foresee the future.

If these fixes do not work, you need a new unibody assembly or keyboard**. The keyboard is available, but Apple does not sell it individually so they tend to be used, clones or manufactured during the “third shift”.

**This was an answer of it’s time, and that stood true for a while. That just isn’t true anymore pre-Retina as the keyboards have been available for years.

Refer to this guide to remove the upper case: MacBook Pro 17" Unibody Upper Case Replacement

Once it is removed, then you can either change the entire unit, or replace the keyboard.