Mac hardware analysis tool: how it works

Hardware problems with computers occur again and again. The Apple Hardware Test is a tool for analysis on Mac computers. We show you how to use it.

Apple Hardware Test (AHT) - Dependency on the operating system version

Depending on the OS X version, the AHT is located in different locations:

• OS X 10.5.4 (Leopard) and older: On the 1st DVD of the supplied DVD set. The DVD must be inserted into the integrated DVD drive before starting the test.
• OS X 10.5.5 (Leopard) to 10.6.7 (Snow Leopard): On the 2nd DVD of the supplied DVD set. The DVD must be inserted into the integrated DVD drive before starting the test.
• OS X 10.7 (Lion) and newer: The AHT is installed on a hard disk partition of the computer.
• Mac computers (from mid-2012) use the integrated "Apple Diagnostic" tool. The program start and execution essentially correspond to the following procedure. See also: support.apple.com/kb/HT5781

Start Apple Hardware Test

To start the Diagnostic Tool, proceed as follows:

1. Since the Mac can get very warm during the test run, ensure there is sufficient air circulation. MacBooks should be powered by the power adapter during the test run so that the computer does not shut down due to an empty battery during the test.
2. If necessary, insert the appropriate DVD and shut down the system.
3. Remove all devices connected to the Mac (exception: wired keyboard and mouse) and the network connection.
4. Start the Mac and immediately press the [D] key on the keyboard (while the screen is still black). Hold it down until the screen turns dark gray.
5. After a few seconds, a small animated icon appears, followed by the start menu of the test.
6. Select the desired language and confirm with [Enter].
7. Wait for the automatic hardware detection and then decide whether you want to carry out the faster or the more detailed test. The detailed test can take 1.5 hours for an i5 (2.8) GHz and 12 MB RAM, for example.
8. Start the test by clicking the [Test] button.
9. As soon as the test is finished, the result is shown in the "Test results" window.

Evaluate Apple Hardware Test

If the AHT finds errors, these are output as codes. Example: 4MOT / 4/40000003: HDD-1240. Unfortunately, only Apple Support can diagnose the hardware errors accurately. However, the first 4 characters of the error code already give an indication of the hardware component concerned. Here is a small selection:

• 4ETH: network adapter
• 4IRP: motherboard
• 4MLB: Logic board controller
• 4PRC: processor
• 4HDD: hard disk
• 4YDC: graphics card
• 4SNS: system sensor
• 4MOT: fan
• 4MEM: RAM
• 4AIR: AirPort WLAN adapter

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