Causes of Mac Hardware Failures
Some Mac issues, such as those involving startup problems, can be caused by software or hardware issues. A good example is getting stuck at the blue screen or gray screen when you start a Mac. The reason the Mac is stuck could be a hardware or software problem. Running the Apple Hardware Test can narrow down the cause. Apple hardware fails from time to time, with the most common failure being RAM. For most Macs, RAM is easy to replace, and running the Apple Hardware Test to confirm a RAM failure is a simple task.
Apple Hardware Test Availability
Not all Macs run AHT. Of those that do, the method differs depending on the operating system version installed on the Mac.
Macs manufactured in 2012 and earlier with OS X Mountain Lion (10.8.4) or later installed have the Apple Hardware Test built into the Mac.Macs made in 2012 and earlier with OS X Mountain Lion (10.8.3) or earlier installed use the system software disc or flash drive that came with the Mac.Macs manufactured in 2013 and later aren’t compatible with AHT.
AHT on Macs That Shipped With OS X Lion or Later
OS X Lion was released in the summer of 2011. Lion marked the change from distributing OS software on physical media (DVDs) to providing the software as a download. Before OS X Lion, the Apple Hardware Test was provided on one of the install DVDs that were included with the Mac. It was also included on a USB flash drive for the early version of the MacBook Air, which didn’t have an optical media slot. With OS X Lion and later, for any Mac manufactured before 2013, the AHT is included in a hidden partition on the Mac’s startup drive. If the Mac has Lion or later installed, you’re set to run the Apple Hardware Test.
AHT on Macs That Shipped With OS X Leopard to OS X Snow Leopard
OS X Leopard (10.5) was released in September 2008. For Macs that were sold with OS X 10.5.5 and later versions of Leopard or with any version of OS X Snow Leopard (10.6), the AHT is located on the Application Install Disc 2 DVD included with the Mac. MacBook Air owners who purchased their Macs during this time frame can find the AHT on the MacBook Air Reinstall Drive. It’s the USB flash drive included with the purchase.
AHT on Intel-Based Macs With OS X Leopard 10.5.4 or Earlier
If you purchased an Intel-based Mac in or before the summer of 2008, the AHT is found on the Mac OS X Install Disc 1 DVD included with the purchase.
AHT on PowerPC-Based Macs
For older Macs, such as iBooks, Power Macs, and PowerBooks, the AHT is on a separate CD included with the Mac.
How to Run the Apple Hardware Test
Now that you know where the AHT is located, you can start the Apple Hardware Test.
Apple Hardware Test Error Codes
The error codes generated by the Apple Hardware Test tend to be cryptic and are meant for Apple service technicians. Many of the error codes are well known, however, and this list may be helpful: You can perform additional troubleshooting for memory (RAM), hard disk, and external disk problems. In the case of a drive, whether internal or external, repair it using Disk Utility, which is included with OS X, or a third-party app such as DiskWarrior or Techtool Pro. If the Mac has user-serviceable RAM modules, clean and reseat the RAM. Remove the RAM, use a pencil eraser to clean the RAM modules’ contacts, and reinstall the RAM. Then, rerun the Apple Hardware Test using the extended testing option. If the Mac still has memory issues, you may need to replace the RAM.
What to Do If You Can’t Find the AHT Disk or USB Flash Drive
If you misplaced the optical media or USB flash drive, you have two choices. You can either take the Mac to the nearest Apple Store or call Apple and order a replacement disk set. Before you call, you need the Mac’s serial number, which is found in the Apple menu under About This Mac. When you have the serial number, call Apple support, or use the online support system to initiate a request for replacement media. The other option is to take the Mac to an Apple Store. The Apple technicians can run the AHT for you and diagnose any problems the Mac has.
