Mac Fixes

How to Run Apple Diagnostics to Fix Your Mac’s Errors

If you suspect that your Mac suffers from hardware issues, then this article is just for you. Luckily, Apple invented a special tool called Apple Diagnostics to help you run a Mac health check. It is a built-in utility available in Macs since 2013. If you’ve got an older Mac, you have Apple Hardware Test, which is a similar tool.


Before we start


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In this article, we will provide you all the information you need about Apple Diagnostics, including:

  1. What is Apple Diagnostics
  2. How to use Apple Diagnostics to fix your Mac’s errors
  3. What if Mac hardware test isn’t running
  4. Error codes that you might encounter
  5. How to fix common errors revealed by Mac systems check

What is Apple Diagnostics

Apple Diagnostics is a tool installed by default on every modern Mac that can be used to detect various hardware errors such as:

  • issues with bad RAM
  • problems with power supply, battery, or power adapter
  • failing sensors
  • graphics problems
  • issues with logic board or CPU
  • wired and wireless Ethernet glitches
  • internal drives and fans misbehavior
  • problems with USB and Bluetooth

Before running Mac diagnostics

1. Make sure that you have an internet connection before starting an Apple Diagnostics test. This will allow you to get recommended support resources, upload the results to Apple, and get access to the Apple support webpage

check that you have network connection

2. Unplug all your external devices such as external hard drives. However, you can keep your mouse, keyboard, and display plugged in

3. If you want to run diagnostics on a MacBook Pro or another portable device, it’s recommended to use a power adapter (AC power source). Testing may drain the battery and cause an unexpected shutdown

How to use Apple Diagnostics to fix your Mac’s errors

Note: Running Apple Hardware Test is quite similar to Apple Diagnostics, and minor differences will be highlighted below where relevant.


1. Turn off your Mac by selecting the Shut Down option from the Apple menu

shut down your mac in apple menu

2. Boot your Mac and hold the D key during the startup to get into the Mac system diagnostics mode

3. Select your preferred test language

  • This step might not appear if Apple Diagnostics already knows your language
  • In Apple Hardware Test, you’ll need to press arrows and Enter key to select a language

4. Run the test

  • In Apple Diagnostics, the check-up will start automatically; you’ll see a progress bar and a remaining time estimation
  • During the Apple Hardware Test, you’ll need to click the Test button or Enter key. Before that, you can select Perform extended testing for a more thorough check-up
status bar in apple diagnostics test

 5. After Apple Diagnostics finishes, you’ll get one of the following two messages on the screen:

  • If your Mac works fine, you will see the No issues found message. If you still suspect problems with your Mac, you can run the test again just to be more certain
  • If there are some issues with your Mac, then you will see a brief description of them together with one or more reference codes and additional instructions. If so, write down these generated error codes. We’ll talk about their meaning in the next section

6. After writing down your error, exit Apple Diagnostics by clicking Restart or Shut Down at the bottom of the screen, or simply press S (Shut Down) or R (Restart). If you would like to re-run the test, press Command (⌘) + R

What if Mac diagnostics system check is not starting

Using a firmware password can prevent Mac diagnostics from starting. Therefore, you need to turn off the firmware password and you can easily do so by following these steps:

  1. Start up your Mac and hold Command (⌘) + R to enter Recovery mode
  2. Enter your firmware password
  3. Click Utilities form the menu bar and choose Firmware Password Utility / Startup Security Utility
  4. Click Turn Off Firmware Password
  5. Enter your firmware password

You’re done. Now you can restart your Mac

Apple Hardware Test error codes

Note: The following codes are the same in Apple Hardware Test and Apple Diagnostics.


Here are the descriptions of error codes you might encounter:

Error codeDescription
ADP000No issues found
CNW001 - CNW006Wi-Fi hardware problems
CNW007- CNW008No Wi-Fi networks detected
NDC001 - NDC006Camera issues
NDD001USB hardware issues
NDK001 - NDK004Keyboard issues
NDL001Bluetooth hardware issues
NDR001 - NDR004Trackpad problems
NDT001 - NDT006Thunderbolt hardware problems
NNN001No serial number detected
PFM001 - PFM007System Management Controller problems
PFR001Mac firmware issue
PPF001 - PPF004Fan problem
PPM001Memory module issue
PPM002 - PPM015Onboard memory problem
PPP001 - PPP003Power adapter issue
PPP007Power adapter not tested
PPR001Processor problem
PPT001Battery not detected
PPT002 - PPT003Battery needs to be replaced soon
PPT004Battery requires service
PPT005Battery not installed correctly
PPT006Battery requires service
PPT007Battery needs to be replaced soon
VDC001 - VDC007SD Card reader issues
VDH002 - VDH004Storage device issue
VDH005Can't start OS X recovery
VFD001 - VFD005Display issues encountered
VFD006Graphics processor problems
VFD007Display issues encountered
VFF001Audio hardware problems
4AIRAirport wireless card problems
4ETHEthernet issues
4HDDHard disk or SSD problems
4IRPLogic board problems
4MEMRAM problems
4MHDExternal disk issues
4MLBLogic board controller problems
4MOTFans problems
4PRCProcessor problems
4SNSSensor issues
4YDCGraphic card problems

How to fix errors revealed by Mac diagnostic test

In case of issues occurring, Apple Diagnostics will offer you to send the error codes to Apple support for repairing or servicing your Mac.


To send the error code to Apple support:

  1. Click the Get Started link. This will restart your Mac in the Recovery mode, and then Safari will open with the Apple Service & Support web page
  2. Click Agree to send the link
  3. When Apple receives your code, it will show additional information about the issue and the steps that you can take to resolve the problems

However, there are some hardware problems you can overcome yourself. Just check our detailed guides:

Fix common errors using resets

After doing a hardware test on your MacBook Pro, iMac, or another Mac model you might be experiencing issues with settings stored in NVRAM, PRAM, or SMC.


What are they? PRAM and NVRAM are special types of memory found on Macs that store system settings such as sound volume, time zone, display resolution and brightness, startup disk selection, and many more. SMC (System Management Controller) is a subsystem that controls your Mac’s temperature and power, batteries, hibernation and sleep, and so on.


In most scenarios, resetting them will help to fix your errors.


If you are using a firmware password, first, you need to turn it off. Follow the instructions mentioned in the previous section.


After turning off your firmware password, you can follow these steps to reset your NVRAM:

  1. Restart your Mac
  2. Crack your knuckles and be ready to hold Option + Command (⌘) + P + R Keys for about 20 seconds during booting
  3. During these 20 seconds, your Mac might appear to restart. It’s completely fine
  4. You can release the keys whenever you hear the startup sound, or when the Apple logo appears and disappears for the second time

Congratulations! You successfully managed to reset your NVRAM/PRAM


Resetting your NVRAM can reset some of your settings, so you might need to go to System Preferences to adjust any settings that were reset

Reset SMC

First, you need to know if your Mac has an Apple T2 security chip. To do so:

  1. Open Apple Menu by clicking on the Apple logo in the upper left corner of the screen
  2. Press and hold Option while clicking on System Information
open system information from the applications folder

3. Select Controller, or iBridge from the Sidebar

4. If you can see Apple T2 chip on the right next to Model Name, then you can follow the T2 method

If you have a T2 chip, use one of the methods below:

1. Reset SMC for laptop computers with a T2 security chip

  1. Shut down your Mac
  2. Press and hold the Power button for 10 seconds
  3. Wait a few seconds, then turn on your Mac

2. Reset SMC for desktop computers with a T2 security chip

  1. Shut down your Mac, then unplug the power cord
  2. Wait for 15 seconds, then plug the power cord back
  3. Wait for 5 seconds, then turn on your Mac

If you don’t have a T2 chip, you can try one of the following methods:

1. Reset SMC for laptop computers with non-removable batteries

  1. Shut down your Mac
  2. Press and hold Shift + Control + Option + Power buttons
  3. Keep holding these keys for about 10 seconds
  4. After holding for 10 seconds, release all the keys and turn on your Mac

2. Reset SMC for laptop computers with removable batteries

  1. Shut down your Mac
  2. Remove the battery (you can contact an Apple store or an Apple-authorized service provider if you need help)
  3. Press and hold the Power button for 5 seconds
  4. Reinstall the battery
  5. Turn on your Mac

3. Reset SMC for desktop computers

  • Shut down your Mac, then unplug the power cord
  • Wait for 15 seconds, then plug the power cord back
  • Wait for 5 seconds, then turn on your Mac

Apple Diagnostics is a simple way to reveal the most common Mac hardware problems. However, sometimes it may not detect particularly rare or specific issues, showing you the No issues found message while the problem exists. In this case, you should contact Apple Support directly or take your Mac to the Apple Store for thorough diagnostics.


You might also encounter software-related problems with macOS. Those will require a different approach to fix. 


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