iMac panic CPU CATERR detected

I agree with kaufmann87's recommendation regarding the RAM. Remove the additional RAM and use run with the original Apple RAM for a bit to see if the crashes continue.

If you have to replace the RAM do so from either Crucial.com or OWC (MacSales.com). They test their modules in each model they are designed for and guarantee compatibility.

With each new system it seems that Macs are more particular about the quality of RAM.

Uninstall the RAM that you installed, low quality RAM has a habit of failing and causing KP's. Most experienced users on these forums will only recommend (and use) either Crucial.com or Macsales.com RAM.

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again. 

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click How to use the Add Text Feature When Post… - Apple Community

does it do this with devices connected outside of OEM mouse and keyboard?

remove all other devices

reset the SMC repeat 3x

and PRAM repeat 3x

SMC and PRAM reset are explained in this article

https://support.apple.com/en-us/HT201295

The most likely suspect is the Norton software. First, there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This documents describe what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community and Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support.  

There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   

Anti Virus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.

There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is designed solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  

Also, unless you're using a true VPN tunnel, such as between you and your employer, school or bank's servers, they are useless from a privacy standpoint.  Read these two articles: Public VPN's are anything but private and Former Malware Distributor Kape Technologies Now Owns ExpressVPN, CyberGhost, Private Internet Access, Zenmate, and a Collection of VPN “Review” Websites. 

That being said, uninstall the Norton/Symantec software according to the developer's instructions. I believe it came with an uninstaller so use it. You can check to see if you've removed all of the supporting files by downloading and running the shareware app Find Any File to search for any files with the application's or the developer's name in the file name.  For the Symantec software you'd do the following search(es): 

1 - Name contains symantec

Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.

FAF can search areas that Spotlight can't like invisible folders, system folders and packages.  

Unless you're using VPN for work, school or banking uninstall it also. It's false security.

Hi everyone,

Just to add to this. I have a 27 inch 2020 core i7 iMac as well (same spec 8gb video card) which has been acting weird lately.

I already had same CATERR kernel panic and haven’t installed external ram nor opened it for whatever reason.

Also the only thing I have installed is a Wacom tablet (the 3th Mac that uses that same tablet bought 3 years ago and never had an issue) and I regularly use the Adobe suite (Though this is 7th iMac in my office to use it and never had issues)

It was running Monterey and had issues with finder, the session closed on their own so things in progress got lost, preview of files wouldn’t load, etc.

So 3 months ago decided to do a clean install of Ventura and a month ago had the first CATERR kernel panic, the computer freezes, the screen turns green and then off. It is necessary to turn the iMac “off” by holding the power button since it doesn’t respond to anything, it has happened on different scenarios around 4 times already no matter if it is being used or it is sleeping. Luckily it still has apple care and tomorrow they will look after it.

Will update if they find something.

Pd. weird enough one of the other iMacs, a 2019 27” base core i5 also started acting weird on finder on Ventura. That one failed out of warranty a year ago and decided to open it for myself since Apple “couldn’t find the problem”. that one had various kernel panics on a daily basis but wiping everything would solve the problem for around a month so I thought it was the ancient HDD on the Fusion Drive and luckily I was right.

Will update if CATERR happens to it as well while on Ventura but I suspect the problem goes beyond software and some 2020 iMacs have either a bad cpu or gpu (yay).

Did you install the additional RAM yourself or did it come with the extra RAM?

If you did it yourself where did you get it, i.e. brand and where bought?

OT has it correct, the AV app at best is 100% worthless and likely the art of your problem. Please located the developers uninstall instructions and then follow to the letter. Then restart the computer in Safe Mode and then restart normally and test.

Also, there is no evidence that you backup your computer. This practice is a 100% guarantee you will lose data. You should be using Time Machine to back up! If you are unfamiliar with Time Machine please click Back up your Mac with Time Machine - Apple Support and begin backing up. You will need an external HD, many experienced users recommend the OWC Mercury Elite Pro due to its reliability, reasonable pricing and the service provided by the vendor.

We would need to see a fresh EtreCheck report to verify that Norton is 100% gone. If it is not then you will need to download the free version of FindAnyFile and have it look for anything that says Norton or Symantec and then have it move those files to the Trash and empty the Trash.

Even when purchasing memory from Crucial, make sure to use the tools on the Crucial website to properly identify the exact memory which is compatible with your computer. Make sure to only order the exact part numbers Crucial identified as compatible with your computer. Do not purchase memory based only on the speed of the memory as that is not enough to ensure compatibility since there are other timings which are not listed by Apple which are critical for compatibility.

If you end up ordering Crucial memory from a third party reseller, make sure to only order the exact part numbers Crucial shows as compatible. Legitimate resellers will list the exact part numbers when ordering and will explicitly mention Mac Compatibility in the product details of that explicit part number.

The kernel panic issues that I had in mid-January and early February were actually caused by issues with the USB-C adapter's internal components, which required the adapter to be replaced. In addition, the computer's logic board was cleaned. I have had no unexpected shutdowns on my computer for the past 2 weeks.

Argh, you also installed a third party VPN app. Please use FindAnyFile and have it search for anything that has NordVPN in it and install.

You really have made a mess of the computer with the stuff you have installed on it. My guess is you may have been a recent convert from MS Windows to Mac OS. If so, please NEVER EVER install third party antivirus, cleaning, security, VPN and other similar types of "maintenance" apps. At best they are 100% unnecessary and at worst can damage Mac OS and cause your Mac to appear buggy and provide similar performance to the type you are experiencing!

Hello everyone. Just to add to this but my MacBook had a similar problem between January 15 and January 18, 2023. This problem began to go away after January 20 with the reinstallation of the OS. The most recent panic occurred on January 21 and the most recent unexpected shutdown happened on January 22 and both of those times it happened while in diagnostic mode.