10.15.4 Supplemental Update Bricking Small Number of T2 Macs

Did you Install the 10.15.4 Supplemental Update on your T2 Mac, only to find that it will not power up after the Install?

When reporting on issues, I always try to quantify the issue in terms of how many users could be affected. In this particular case, the numbers are very low. This article is to help you rescue your Mac. The issue only affects T2 Macs that have installed the 10.15.4 Supplemental Update. The amount of users reporting this is very small, but the problem can be devastating if the user does not understand what happened or how to fix it.

This issue is similar to the 2019-001 Security Update last November that cause Data loss. The Reports are very close as it was first thought that the problem was the users fault for shutting down the Mac during the BridgeOS update.

What actually happened was, the BridgeOS Update Failed and destroyed the encryption keys.

mrmacintosh.com/mojave-2019-001-security-update-causing-data-loss-if-interrupted/

1. Affected Mac Models
2. Affected OS Versions
3. Problem: 10.15.4 Supplemental BridgeOS Update
4. Problem Description
5. Can the dead Mac be brought back to life? YES!
6. Why write about something that affects such a small number of Macs?
7. Wait a few days before installing updates.
8. Should I block the 10.15.4 Supplemental Update?
9. Does Apple Know about this issue and are they working on a fix?
10. Links
11. Credit & Hat Tips

1. Affected Mac Models

This issue covers almost every single T2 Mac Model. I have not seen any reports of this happening to the iMac Pro 2017 or the Mac Pro 2019.

1. MacBook Pro 16′ 2019
2. MacBook Pro 13″ & 15″ 2018-2019
3. MacBook Air 2018-2020
4. Mac Mini 2018

2. Affected OS Versions

This issue affects only one macOS update.

macOS Catalina 10.15.4 Supplemental Update (19E287) Released 4/8/20

3. Problem: 10.15.4 Supplemental Update Bricked

One of the very first reports was in a MacAdmins Channel. The report said that the user called the helpdesk saying the update hung. Now the Mac does not power on.

Another report from a user with a 2018 13″ MacBook Pro

I attempted to install the update but about halfway through my computer shutdown and it bricked my 2018 13 inch MacBook. No power, no fans coming on and off or anything when pressing and holding the power button.

Another Report from a 16″ Macbook Pro 2019 User.

Confirmed; this is what happened to my 16″ after this install. I needed to do a DFU restore (using Apple Configurator 2 — you can download it to your hopefully spare MacBook from the app store) to get my mac back up and running. Unfortunately, for some reason, after the DFU restore, my 16″ came back up to do a full reinstall, and I had to restore my files from backup.

One More report form a 13″ MacBook Pro User

Anyone else do the recent 10.15.4 update and have their machine completely bricked? Mine will not turn on…not after resetting the SMB…not at all. Apple’s update appears to have completely killed my macbook. It’s now completely unresponsive.

Macbook Air 2018 User

Thursday evening my wife’s Air still showed the update in System Prefs and clicked to install it. She said the dialog box said it was normal for the screen to go black, but it didn’t say it’d never come back!!! Her less than 18 month old Air is now officially bricked. Unresponsive to all attempts to remind it of its mission on earth. A stellar machine until that fateful click.

4. Problem Description

Apple’s T2 Security chip runs software called BridgeOS. That software is updated each time you install a Catalina Update or Security Update. The T2 controls many aspects of your Mac.

The Apple T2 Security Chip is Apple’s second-generation, custom silicon for Mac. By redesigning and integrating several controllers found in other Mac computers—such as the System Management Controller, image signal processor, audio controller, and SSD controller—the T2 chip delivers new capabilities to your Mac
Apple.com HT208862

If the update to BridgeOS fails, it can prevent your Mac from booting. This exactly what happened to some users.

You can read more about the T2 Security Chip from the links below.

support.apple.com/en-us/HT208862

apple.com/euro/mac/shared/docs/Apple_T2_Security_Chip_Overview.pdf

michaellynn.github.io/2018/07/27/booting-secure/

After reading through a bunch of reports the problem seems happen during the BridgeOS Update phase. Most users say that all they saw was a black screen and the Mac was unresponsive. From the users who contacted me over email, after the update failed the Mac was already be in DFU mode. A few users stated that as soon as they connected the dead Mac to a host mac with Apple Configuartor 2 running, it immediately showed up in RECOVERY Mode.

5. Can the dead Mac be brought back to life? YES!

In almost every case, a DFU Mode BridgeOS Reinstall brought these dead Macs back to life!

I wrote a detailed article on how to perform the restore below.

mrmacintosh.com/how-to-restore-bridgeos-on-a-t2-mac-how-to-put-a-mac-into-dfu-mode/

I knew something was up on April 10th two days after the supplemental update was released. I noticed a spike in traffic to my BridgeOS Restore article. Emails and comments started to roll in. They all mentioned that they found the article after the 10.15.4 Supplemental Update bricked their Mac.

6. Why write about something that affects such a small number of Macs?

Like I mentioned at the top of this article, I usually will only report on issues that affect a large number of Mac Users. The idea is that small fluke type issues happen all the time. Usually the user can just reinstall macOS and be up and running.

This case was different. I decided to write this article after reading some of the stories.

Haven’t talked with Apple’s help team since 2004—today we spent 2 hours on the phone—we tried every method to get my bricked 2018 15” MacBook Pro to boot. Hopefully this issue is a small epidemic and not a pandemic; the MBP became unresponsive today while updating to 10.15.4. The last thing I saw before the MBP went quiet and the screen went black was, “about 14 minutes remaining”. Apple Help quoted $815 to ship it to them for a diagnostic and repair. I explained it was working perfectly well before the update—CSR elevated it to a senior who is starting with a new charger and cable.

Here is another direct quote from a 2018 Mac Mini User that I found tonight.

Any one else experienced this problem? Mac mini late 2018. Update went through, restarted Mac and now bricked. Will not turn on at all. Took it to Apple store and they say main board needs replacing at cost of 400usd.

I hope this article finds you mattoneill2! ^

If this article can save just a few Mac Users from having to spend $$$ for a repair, then it was definitely worth it.

7. Wait a few days before installing updates.

A good tip for you is to just wait a few days for the dust to settle before installing updates.

This is not the first time Apple has pulled an update. They pulled High Sierra and Sierra 2019-002 Security Update this past March. It’s a good idea to wait at least a few days before you update.

mrmacintosh.com/apple-replaces-2019-002-security-updates-for-10-13-and-10-12-bridgeos-updates-also-show-as-new/

Another example is the GPU Freezing Issue that I noted above

mrmacintosh.com/2020-002-update-causes-some-macs-to-freeze-when-using-video-conf-apps/

8. Should I block the 10.15.4 Supplemental Update?

Maybe

The only reason I say maybe, is that the supplemental update does not include any Security Related fixes. Take a look at the list below.

Fixes an issue where Mac computers running macOS Catalina 10.15.4 could not participate in FaceTime calls with devices running iOS 9.3.6 and earlier or OS X El Capitan 10.11.6 and earlier
Resolves an issue where you may repeatedly receive a password prompt for an Office 365 account
Fixes an issue where MacBook Air (Retina, 13-inch, 2020) may hang in Setup Assistant or when disconnecting and reconnecting a 4K or 5K external display
Resolves an issue where a USB-C port in your Mac may become unresponsive

If you need any of the above fixes, then I would say deploy it. The risk is really low.

9. Does Apple Know about this issue? Are they working on a fix?

Unlike the GPU freezing issue or the Wake from Sleep issue, I do not have any information.

10. Links

Apple Support Forum

MacRumors.com

Reddit.com

HackerNews

https://news.ycombinator.com/item?id=22845629

11. Credits – Hat Tips

MrMacintosh Readers who posted comments and emailed me about this issue.

10.15.4 Supplemental Update Bricked

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