For some years now, the only way that your Mac can update its firmware is when you install a macOS update – which includes both updates to macOS as a whole, and Security Updates for previous major releases of macOS. Each such update now comes with installers for the current release versions of firmware, which are different for various models of Mac.

Keeping your Mac’s firmware up to date is important. Old versions can have incompatibilities with more recent releases of macOS (or Security Updates), and may contain security vulnerabilities and other bugs. When everything works well, you shouldn’t have to worry about any of this. You let Software Update download and install macOS updates, and whenever new firmware is released for your particular model, that gets updated too.

Occasionally, though, updaters don’t install the firmware updates they’re expected to. When this happens once, it’s no great disaster, and applying the update a second time – perhaps in the ‘Combo’ updater – often does the trick. It’s not as convenient, perhaps, as being able to run a separate firmware installer, but works.

Since the release of the first version of Catalina six months ago, one particular model has resulted in a worryingly high failure rate in firmware updates: the iMac Retina 5K 27-inch Late 2015 (iMac17,1). Those iMacs should have been updated from version 170.0.0.0 to 173.0.0.0 when upgraded to Catalina, or with the matching Security Update for those which remained on High Sierra or Mojave. Readers here reported this problem, and I posted an article which questioned what was going on.

There have been at least two further firmware updates for that model since, with 10.15.3 (and Security Updates) taking it to 175.0.0.0, and 10.15.4 (and Security Updates) on to 176.0.0.0. Yet some users have continued to report that the version number of their iMac17,1 firmware has remained stuck at 170.0.0.0.

Following that last update, I asked you to let me know the current firmware version of any iMac17,1 which had been updated to 10.15.4, or using Security Updates 2020-002 containing the same firmware update. I’ve now had information for a total of 59 different iMacs, for which I’d like to thank all those who have so generously responded. This clearly isn’t a random sample by any means, but only 27 of those 59 – that’s 46% – are now running 176.0.0.0, the current firmware.

My figures broken down by current macOS version are:

• High Sierra – the one report I have is now at 176.0.0.0
• Mojave – of the 9 reports, 6 are stuck at 170.0.0.0, and 3 are at 176.0.0.0
• Catalina – of the 45 reports, 14 are stuck at 170.0.0.0, 1 at 173.0.0.0, 10 at 175.0.0.0, and only 20 have made it to 176.0.0.0
• In 4 reports, I don’t know which version of macOS they’re running, but 1 is still at 170.0.0.0, and 3 at 176.0.0.0.

Overall, that totals 21 (36%) at 170.0.0.0, 1 at 173.0.0.0, 10 at 175.0.0.0, and 27 (46%) at 176.0.0.0. In other words, in many cases the firmware of iMac17,1 models isn’t being updated correctly even after several attempts to do so.

I don’t know why this is happening, nor why the installer isn’t reporting the error to the user. Other than downloading and installing a standalone installer, either for the basic installation, or the ‘Combo’ update, there’s nothing else that the user can do. I have therefore compiled a short report for Apple and posted it to the Feedback system. This will hopefully enable Apple’s engineers to get these updates working more reliably.

If you want to check whether your Mac is running the latest firmware, I’m afraid Apple doesn’t publish a list of which versions are current. Thanks to the help of readers here, particularly Pico, I maintain lists covering all models, and for some older versions of macOS too. For recent models, the simplest way to check your Mac is using my free SilentKnight. This automatically reads the firmware version and compares it with that stored in my GitHub database. If you’d prefer to do it manually, then this article gives full details.

If you think that another model has similar problems to the iMac17,1, don’t hesitate to let me know.

Thank you again to all who responded to my previous request: I hope that your effort brings a solution.