The Apple Hardware Test (AHT) can help you find problems with your Mac

The Apple Hardware Test (AHT) is a comprehensive application that can help diagnose hardware-related issues you may have with your Mac.

Some Mac problems, such as those related to startup, can be caused by software or hardware issues. A good example is getting stuck on the blue or gray screen when you start up your Mac. The reason you’re stuck could be a hardware or software issue; running Apple’s hardware test can help you narrow down the cause.

The AHT can diagnose problems with your Mac’s display, graphics, processor, memory, logic card, sensors, and storage.

While we don’t like to think of this happening, Apple hardware fails from time to time, with the most common failure being RAM. Fortunately, for most Macs, RAM is easy to replace; running Apple’s hardware test to confirm a RAM failure is a fairly simple task.

There are several ways to run the AHT, including a method to upload the test from the Internet. But not all Macs are compatible with Apple’s hardware test over the Internet; this is especially true of pre-2010 Macs. To test an older Mac, you first need to determine where the AHT is located.

Where is Apple’s hardware test located?

The location of the AHT depends on the model and year of your Mac. The process of getting the AHT up and running also depends on the Mac you are testing.

2013 or newer Macs

For all Macs from 2013 and later, Apple changed the hardware testing system to use a new hardware testing system called Apple Diagnostics. Be sure to read the instructions for use of the new system.

Macs that ship with OS X Lion or later

OS X Lion was released in the summer of 2011. Lion marked the shift from distributing OS software on physical media (DVD) to providing the software as a download. Before OS X Lion, Apple’s hardware test was done on one of the installation DVDs that came with your Mac, or on a special USB flash drive that came with the first version of the MacBook Air, which didn’t have a optical media slot.

With OS X Lion and later, the AHT is included in a hidden partition on a Mac’s startup drive. If you’re using Lion or later, you’re ready to run Apple’s hardware test; just skip to the How To Run AHT section.

Note : If you’ve erased or replaced your Mac’s startup drive, you’ll probably need to use Apple’s online hardware test.

Macs that shipped with OS X 10.5.5 (Fall 2008) through OS X 10.6.7 (Summer 2011)

OS X (Leopard) was released in September 2008. For Macs that shipped with OS X 10.5.5 and later versions of Leopard, or any version of Snow Leopard, the AHT is located on the Application Install DVD Disc 2 that is included with the Mac.

MacBook Air owners who purchased their Macs during this time period will find the AHT in the MacBook Air Reinstall Drive, a USB flash drive included with purchase.

Intel-based Macs purchased with OS X 10.5.4 (Summer 2008) or earlier

If you got your Mac in the summer of 2008 or earlier, you’ll find the AHT on the Mac OS X Disc 1 Setup DVD that came with your purchase.

PowerPC-based Macs

For older Macs, such as iBooks, Power Macs, and PowerBooks, the AHT is on a separate CD that came with your Mac. If you can’t find the CD, you can download the AHT and burn a copy to CD. You’ll find the AHT and instructions for burning a CD on the Apple Hardware Test Images website.

What to do if you can’t find the AHT disk or USB flash drive

It is not uncommon for optical media or USB flash drive to get lost over time. And of course, you won’t notice they’re missing until you need them.

If you find yourself in this situation, you have two basic options. You can call Apple and order a replacement set of drives. You’ll need your Mac’s serial number; Here’s how to find it:

  1. From the Apple menu, select About This Mac .
  2. When the About This Mac window opens, click the text between OS X and the Software Update button.
  3. With each click, the text will change to display the current version of OS X, the OS X build number, or the serial number.

Once you have the serial number, you can call Apple Support at 1-800-APL-CARE or use the online support system to initiate a request for replacement media.

The other option is to take your Mac to an Apple Authorized Service Center or Apple Retail Store. They should be able to run the AHT for you, as well as help diagnose any problems you’re having.

How to run the Apple Hardware Test

Now that you know where the AHT is, we can start Apple’s hardware test.

  1. Insert the appropriate DVD or USB flash drive into your Mac.
  2. Shut down your Mac, if it’s on.
  3. If you’re testing a Mac notebook, be sure to connect it to an AC power source. Don’t test using the Mac’s battery.
  4. Press the power button to start your Mac.
  5. Immediately hold down the D key . Make sure the D key is pressed before a gray screen appears. If the gray screen wins you over, wait for your Mac to start up, then shut it down and repeat the process.
  6. Hold down the D key until you see a small icon of a Mac on your screen. Once you see the icon, you can release the D key .
  7. A list of languages ​​that can be used to run the AHT will appear. Use your mouse cursor or the Up/Down arrow keys to highlight the language you want to use, then click the button in the lower right corner (the one with the arrow pointing to the right).
  8. Apple’s hardware test will check what hardware is installed on your Mac. You may have to wait a bit for the hardware probe to complete. Once complete, the Test button will light up.
  1. Before pressing the Test button , you can check the test hardware by clicking the Hardware Profile tab . Review the list of components to make sure the main components of your Mac are listed correctly. If something seems wrong, you should check what your Mac’s settings should be. To do this, check Apple’s support site for the specifications of the Mac you’re using. If the configuration information does not match, you may have a faulty device that will need to be checked and repaired or replaced.
  2. If the configuration information appears to be correct, you can proceed to the test.
  3. Click the Hardware Test tab .
  4. The AHT supports two types of tests: a standard test and an extended test. The extended test is a good way to find problems with RAM or graphics. But even if you suspect such a problem, it’s probably a good idea to start with the shorter standard test.
  5. Click the Test button .
  6. The AHT will start, displaying a status bar and any error messages that may result. The test may take a while, so sit back or take a break. You may hear your Mac’s fans speed up and down; this is normal during the testing process.
  1. The status bar will disappear when the test is complete. The Test Results area of ​​the window will display a “No Problems Found” message or a list of problems found. If you see an error in your test results, take a look at the error code section below for a list of common error codes and what they mean.
  2. If everything seems fine, you may want to run the extended test, which is better at finding memory and graphics issues. To run the extended test, check the Perform Extended Testing box (takes significantly longer) and click the Test button .

Ending a test in progress

You can stop any test in progress by clicking the Stop Test button .

Exit Apple Hardware Test

After you have finished using the Apple Hardware Test, you can exit the test by clicking the Restart or Shut Down button .

Apple Hardware Test Error Codes

The error codes generated by the Apple Hardware Test tend to be cryptic at best and are intended for Apple service technicians. However, many of the error codes have become very well known, and the following list should be helpful:

Error Code Description 4AIR AirPort Wireless Card 4ETH Ethernet 4HDD Hard Drive (includes SSD) 4IRP Logic Board 4MEM Memory Module (RAM) 4MHD External Drive 4MLB Logic Board Controller 4MOT Fans 4PRC Processor 4SNS Sensor Failure 4YDC Video/Graphics Card Apple Hardware Test Error Codes

Most of the above error codes indicate a related component failure and may require having your Mac checked out by a technician to determine the cause and cost of repair. But before you send your Mac to a store, try resetting the PRAM as well as the SMC. This can be useful for some errors, including logic board and fan issues.

You can perform additional troubleshooting for memory (RAM), hard drive, and external drive problems. In the case of a drive, be it internal or external, you can try repairing it using Disk Utility (which is included with OS X) or a third-party application such as Drive Genius.

If your Mac has user-serviceable RAM modules, try cleaning and resetting the RAM. Remove the RAM, use a pencil eraser to clean the contacts on the RAM modules, then reinstall the RAM. Once the RAM has been reinstalled, run Apple’s hardware test again, using the extended test option. If you are still experiencing memory issues, you may need to replace your RAM.