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How to run diagnostics on a Mac with ease

6 min read

We associate a Mac with quality, capacity, speed, and reliability. But it might happen so that your Mac underperforms and unpredictable issues occur. Before taking it to the nearest Apple service, you can try to identify the problem by yourself. That will save your time and money, and prevent serious system crashes. Identifying whether the issue is a hardware or software one will determine the possible actions and next steps. 

When we deal with the hardware problem, the first thing to try is to perform Apple Diagnostics (or Apple Hardware Test). It will help you reveal the process that causes the problem and lowers Mac productivity.

Apple Diagnostics is an easy-to-understand tool that provides detailed results and suggestions with the next steps. Whether you are a techie or not, you'll get everything easily.

What is Apple Diagnostics?

Apple Diagnostics is a built-in test that helps detect what hardware components are causing the problem, and find system failures. The test checks RAM, power controller, logic board, battery, and other wireless modules.

That was the hard part. And the easy part is that you can run Apple Diagnostics in just a few steps. The whole process will take about  2-5 minutes —  but ultimately saves  hours of your time. 

A great feature of Apple test is that after hardware checking, it displays an error code, offers you clear solutions, and the assistance of Apple Support. You can write out the error codes (known as reference codes), and either do the research on/ your own or contact Apple.

When referring to Mac hardware test, you might also hear about Apple Hardware Test (AHT). This is an older brother of Apple Diagnostics (AD), and they have some minor differences. Mainly, the results of AHT aren't conclusive and descriptive. AHT is used in Macs released in  2012 or earlier, while AD is a more advanced analog that works with newer Macs. 

Essentially, a Mac hardware test is the great tool to help you understand the problem. And if it doesn't have a fix for it — there are more advanced tools that you can use to troubleshoot Mac issues. More about that in a moment.

How to run Mac diagnostics

Running a hardware test on Mac may seem like a complicated process, but believe us — that's not:

  1. Disconnect all the peripheral devices (printer, cables, external DVD drive) except the keyboard, mouse, display, and speakers. Make sure your Mac is connected to mains power and the internet. 
  2. Select Apple Menu > Restart
  3. Press and hold the D key until you see a list of different languages on the screen
  4. Select a language. Apple Diagnostics starts automatically.
  5. Wait for about 2-5 minutes until the checking is completed. If any problems are found, you'll see the options of solutions and an error code. 

Mac diagnostics

After that, you can either repeat the test, get more information, restart or shut down the Mac. That's it - an easy 5-step process, as promised.

Apple recommends to print out the instructions to keep them close at hand and make sure you don't miss any step. Or, you can take a photo. Right, that's what people do in 2021. 

What are the common Apple Diagnostics results

After performing a Mac hardware test, you'll get the list of found issues with detailed descriptions and related reference codes. Each code stands for a particular error and helps you quickly figure out the next steps. Usually, an error description will suggest possible solutions. However, to fix a specific problem, Apple Diagnostics might recommend you to contact Apple or take your Mac to an Apple Authorised Service Provider or Apple Store.

There could be the case the system testing doesn't find any issues. 

In this case, you have a few options. Please note that they are mutually exclusive, which means you should choose the best option for you:

  1.  Repeat the process by hitting Run the test again
  2. Because well, sometimes a small mistake might hamper it all. Maybe the first time you tried to run Apple Diagnostics, your power adapter wasn't plugged in. Connect it and try again — this will help fix the problem.

  3. To get more information on support and service options, click on Get started:
    • The macOS X recovery will start
    • Send your serial number and reference codes to Apple by clicking Agree to send
    • Follow the on-screen instructions.
  4. Restart your Mac 
  5. Hit the Shut Down button.

What if you can't run diagnostics

You can face the problem when Apple Diagnostics simply doesn't work. Don't worry, it's solvable. There might be a couple of reasons why this happens:

  1. Some external devices are plugged in. Double-check you've disconnected everything except the keyboard, mouse, display, and speakers. 
  2. A part of the diagnostics system can be damaged. You can solve the problem by restarting the Mac while holding down Option+D. This will start an internet-based hardware test.
  3. Firmware password might be the problem. Make sure you turn it off while performing hardware testing.

What if diagnostics found no issues

In case Apple Diagnostics identifies no hardware issues —  but your Mac is still misbehaving —  maybe, software is the problem.

Often, Macs are slowing down, freezing, or behaving strangely due to full storage, malware, leftovers from uninstalled apps, large and old files. The good news is you don't have to guess, or install many applications to fix each problem separately. An all-in-one tool called CleanMyMac X has all the required functions to test your Mac from a to z. It cleans up, protects, and speeds up your Mac.

Just one click to optimize your Mac — CleanMyMac X makes it fly like a rocket.

Here's how CleanMyMac X optimization works:

  1. Go to the Maintenance tab
  2. Specify what should be done. For example, if you want to speed up your Mac by freeing up some space, check the box next to  Free Up Ram”. You can select all the tasks at a time, or choose the particular ones. 
  3. Press Run.

CleanMyMac freeup RAM

Yay, you launched a rocket!

The most common problem that impairs system performance is the junk files that clutter your Mac. You might not even know about them. Luckily, CleanMyMac X has a solution for this, too. Resolve various errors with a great feature called System Junk:

  1. Hit Scan
  2. Once you see the results, press Review Details

CleanMyMac system junk

You'll see the list of all items that should be cleaned or fixed. You can review the results  and deselect those items you're not ready to let go. CleanMyMac X will omit them while cleaning up your Mac. Once you're ready, hit Clean.

CleanMyMac user cache files

Wow, your Mac feels much better now.

Know the reason behind Mac issues

Running Apple Diagnostics is a bit like a shot in the dark. You’re trying to fix something you have no idea about. In some cases, it will work, but you can achieve better results if you know why the issues occur. 

iStat Menus is a utility that sits in the menu bar, with tons of useful real-time insights about your Mac. Check your CPU and GPU usage, memory load, fan speeds, and more in one click. Whenever your Mac is freezing, getting slow, or making loud fan noise, iStat Menus will tell you why it happens. 

iStat Menus macOS system monitors

App Tamer is another utility similar to iStat, but with more focus on idle apps hogging your CPU. See which apps are putting pressure on your Mac and force quit or uninstall them to optimize performance. A nice touch: App Tamer changes its menu icon color when CPU use goes beyond normal. 

App Tamer CPU monitor


System performance testing is a handy tool that keeps your Mac healthy, saves your time and money. The primary step is to understand whether the issue is a hardware or software one. While Apple Diagnostics deals with hardware breakdowns, CleanMyMac can fix the software problems.

Doesn't matter if you are a Mac power user or Mac-newbie, these tools will do system testing and optimization for you. To make the most out of your Mac, regularly check its performance with iStat Menus and App Tamer. 

Running Apple Diagnostics and optimizing performance with CleanMyMac X, iStat Menus, and App Tamer prolongs the life of your Mac. These three apps are free for 7 days on Setapp, the curated suite of best productivity apps — so you can try them all to make your Mac fly.

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