To an average computer user, any challenge with the hardware or even software warrants the need of a technician. This need not be the case and as a matter of fact, it is quite easy to troubleshoot some of the common problems that your PC might be facing. Especially with some of the hardware diagnostic software that we will be discussing, you can be sure that the trips to the technician will be. By knowing your exact Model Identifier (MacBokPro?,?) you could look in to this data base for the correct version of AHT to download.

If you want to check your Mac’s hardware out, the first step is to run Diagnostics or Apple Hardware Test, which are detailed here. When you follow those instructions – disconnect all non-essential peripherals, connect keyboard and mouse/trackpad via USB, hold the D key and start up – eventually you should see the diagnostic test on offer. But what if you don’t?

It’s worth checking that you are following the instructions in detail. Apple recommends that, rather than restarting into Diagnostics, you should enter it after shutting down, preparing your Mac, then starting up. Your Mac also can’t enter Diagnostics while it has a firmware password enabled. You’ll first need to disable that in Recovery mode, then shut down, wait a minute or two, and start up with the D key held.

The fallback if those fail is to ensure that your Mac has both a Wi-Fi and wired Ethernet connection if possible, and repeat the startup with ⌥D (Option-D) instead. This should, provided your Mac can gain an Internet connection, run remote Diagnostics from Apple’s support site instead. You should use both Internet connections if possible, to give this maximum flexibility; you should normally run Diagnostics with a Wi-Fi network available in any case, or its Wi-Fi tests won’t be possible.

Mac models introduced before June 2013 don’t of course run Diagnostics as such, but an older version named Apple Hardware Test, or AHT, and it’s those which are most prone to being unable to run locally, because of the way in which AHT is installed. Indeed, the oldest Intel Macs can’t even run AHT from their boot disk, and you’ll need to insert the original install (optical) disk supplied with that Mac.

Macs that were made between about 2007 and May 2013 normally run AHT from code which is hidden away in /System/Library/CoreServices/.diagnostics, which often seems to get wiped and not restored when you replace the internal storage, or perform a clean re-install. Behringer usb wdm audio driver for mac download. Those can easily leave your Mac relying on remote AHT unless the contents of that folder are replaced.

Unfortunately, because of SIP, restoring a local copy of AHT isn’t easy. You need a copy of the correct version of AHT not just for your Mac model, but for its specific series of logic board. Most users don’t go through the process of trying to put it back in place, but instead install it on a bootable USB memory ‘stick’ instead, where they know that it won’t be at risk of being wiped again. A large collection of links to different versions of AHT and full instructions are provided here.

More recent Macs don’t seem to keep their Diagnostics software in the same location – and those with a T2 chip certainly don’t. I deliberately avoided including the Diagnostics boot process in my summary of booting the Mac, because so little seems to be known about it. But I’d be most surprised if Macs with T2 chips don’t protect their Diagnostics within their Secure Boot process, perhaps even within boot.efi itself.

Unless you enjoy tinkering with macOS internals, if you can’t get your Mac to enter Diagnostics mode using the D key, it’s probably simplest to shrug and use ⌥D (Option-D) instead, and not to worry about restoring its local copy of the Diagnostics or AHT software.

However, if your Mac can’t run Diagnostics locally, you’d also be wise to check that it has a functional Recovery partition, in case that wasn’t configured properly as well. Not only can you test this by trying to start up in Recovery mode, but you should be able to identify it using the
diskutil list
command, where your startup disk should have a volume named Recovery, whether it’s in HFS+ or APFS format. As this isn’t mounted during normal running, you won’t see it in the Finder or Disk Utility.

Replacing a Recovery partition isn’t a simple task either. One example of doing so is given here, and the AppleScript tool to simplify that is available from here.

Problems like these with Diagnostics/AHT and Recovery partitions are unusual, if not downright rare. But when they happen, they are more than inconvenient. Sadly the treatment is usually worse than the illness itself.

In order for OS X or any software to run properly, your Mac’s hardware must first be in running order. While symptoms of crashes, graphical artifacts, or other corruption can be indicators of hardware malfunction, one way to help determine if hardware problems are the root of the issue at hand is to run a hardware test.

When you purchase your Mac from Apple, the system includes hardware tests in a couple of locations. The first is on your boot drive, but in addition if your system came with a gray restore DVD then tests specific to your system will be available on it as well. For those without DVD drives, and those created after 2010, Apple’s Internet Recovery services can be used to download and run applicable hardware tests.

To invoke the hardware tests, insert the restore DVD that came with your system. If your system is new enough that it did not come with a DVD drive, then skip this step. Now perform the following actions:

1. Reboot your Mac
2. Hold the “D” key down immediately when you hear the boot chimes

If your system loads the tests, then for older systems you will see a small image of a computer and a processor chip appear on your screen, followed by an option to choose your language. If this does not appear and the system boots normally, then the tests were not properly loaded. If your Mac supports Internet Recovery, then in step 2 above, you can hold Option-D to force the system to load these tools from the internet, where it will download them from Apple’s servers.

When you have chosen a language, then the hardware tests will load. For older systems you may see a tabbed window on a blue background, with a big button labeled “Test” in the middle of it. Below this button is a checkbox for enabling the extended memory tests, which will scan your installed RAM in great depth. This option may take hours to complete, but is a recommended step to take anytime you have purchased a new system (even brand new from Apple), or have installed new RAM into your system.

When you click the Test button, a progress bar will appear and show you the time remaining for the tests. During the course of the tests, you may hear the system’s fans spin up and down, but this is a normal occurrence, provided the test interface is still responsive (ie, the mouse still moves).

Apple’s latest hardware test versions show a gray scroll bar (click for larger view).

For more modern systems such as the Retina MacBook Pro, you will see a gray progress bar appear that says “Checking your Mac…” with a time-remaining countdown. When this finishes, the system will show you the results of the test.

Interpreting the Tests

Hopefully the tests determine your system is clean and functioning properly; however, if not, then they will display an error code such as the following, to indicate a problem:

4SNS/1/1/4000000 TL0P-130

While this code might seem unintelligible, parts of it can be broken down to determine where the problem lies. The following list of codes show the possible outputs that you might see from the hardware test:

The results of the hardware test, if any, will show here (click for larger view).

4ETH: Ethernet controller
4IRP: Main Logic board
4MLB: Logic board controller
4PRC: Processor
4HDD: Hard disk
4MHD: External disk
4YDC: Video card
4SNS: System sensor
4MOT: Fan motor
4MEM: Memory module
4AIR: AirPort wireless card

From this list, you can see the “4SNS” in the example above means there is a problem with a system sensor, which can be a temperature sensor, a current sensor, or a voltage sensor. Now you can determine which of these is the case by looking at the final detail of the reading (TL0P-130). In this case “T” stands for temperature, but it could also be “I” for current, or “V” for voltage.

The letter following the “T,” “I,” or “V,” lets you know what component of the system the sensor is in. The following list is a breakdown of what each of these components is:

A: Ambient air sensor
B: Battery
C: Central processors (CPU)
D: DC (direct current)
e: PCI-express slot
F: FireWire port
G: Graphics processor (GPU)
H: Hard disk
h: Heat pipe (heat sink)
L: LCD display
M: Memory or memory riser boards
m: Misc. (i.e., battery chargers)
N: North bridge (motherboard controller)
O: Optical drives
P: Power bus
p: Power supply
s: Palm rests for laptops
W: Airport Wi-Fi card

From this detail, we can see the example problem is with a temperature sensor in the LCD display of a MacBook system.

Actions to take

Unfortunately with hardware errors, there is often not much you can do except take the system in to an Apple store to have parts replaced. While some components such as memory and hard drives are user-serviceable in some Macs and can be swapped out, for other components this is not easy to do.

You can try resetting the PRAM or reset the system management controller to see if that helps clear the problem. Otherwise, if the problem is with a Wi-Fi card or optical drive then you can try opening the system to see if relevant components have become dislodged, and then reseat them.

If you are unable to perform these tasks, or feel uncomfortable with opening your system, then take it in to an Apple Store or an authorized Apple Service Center for servicing.