The first thing I'd try is resetting the System Management Controller (SMC).
Reset the SMC
For your model MacBook Air here’s what you do:
- Shut down your computer
- Keep the MagSafe adapter (power cable) plugged in.
- Press at the same time shiftoptioncontrol
(on the left side of the built-in keyboard) and the power button
- Let go
- Turn your computer back on with the power button.
If this has no impact, you can run Apple Hardware Test.
Apple Hardware Test
Your model MacBook Air uses Apple Hardware Test. To use this, follow these steps:
- Shut down your MacBook Air
- Restart your MacBook Air
- Press and hold the D key before the gray startup screen appears.
- After a while, Apple Hardware Test (AHT) will start.
- When prompted, select your language and click the right arrow.
- When the AHT console appears, you can choose to run Basic tests by clicking the
Test button. However, I suggest you select the "Perform extended testing" checkbox
before you click the Test button.
- Your test results will appear in the window in the bottom-right of the console.
Note 1: that the extended test will take some time. Take a note of the results and
Note 2: If pressing and holding the D key at Step 3 doesn't work, start again at Step 1 and, at Step 3 press and hold both the OptionD keys instead. This will try and run diagnostics from the internet instead, so you will need to allow more time for it to complete.
Let me know how you go.