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I have 3 EOS cameras: 2 EOS R's, and 1 EOS R6.  All 3 are showing the error message "Err 01".  I have looked on line and people are saying it is a lens contact issue.  It is true that if you switch to a different lens, it normally fixes itself(after you have removed, then reinstalled the battery.)  

However, it started 1st on one of my EOS R's using my Canon 24-105, f4.  Then within a week, on my 2nd EOS R.  And within the 2nd week, it started effecting my EOS R6.  Then, the same thing started occurring using my Canon 24-70, f2.8.  A unique issue is that sometimes it doesn't happen when shooting at the widest aperture.  But as soon as I stop the lens down 1 stop, it occurs.

I have heard the only cure is to send the lens back for repair to fix an aperture issue.

I don't believe it is a normal prime lens issue, but rather a zoom lens issue on the new Canon EOS cameras.  I used both lenses on my older Canon 5D Mark II for several years without issue.  Then, I switch to the new EOS cameras and both lenses go bad within 2 weeks?  I don't think so.

  I have cleaned the contacts on all the cameras, on the lenses, and the lens converters. And the error message still pops up.

Has anyone else found the same issues?  Or a fix?



Hi and welcome to the forum:

To assist you it would be helpful to have some more detail:

Are the lenses you are using RF lenses or EF lenses via an adapter?

IF you are using an EF-RF adapter, what brand is it?

cheers, TREVOR

Before you ask us, have you looked in the manual or on the Canon Support Site?
"All the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris

Hi Trevor.

All my lenses are EF mounts, and I am using the Canon ER-RF adapter.

I determined that the adapter wasn't the issue, since my prime lenses work fine on all 3 adapters.  Just the zoom lenses don't work.


Hey Trevor! Did you ever get this figured out? I’m having the exact same issue, right down to the unique issue where it doesn’t throw the error when zoomed at the way out or at the largest aperature.


Hi Bmolson. I sent 1 of my lenses back for repair, my 24-70.  It hasn't had the same issue since(almost 6 months).  But I am convinced the issue is with the EOS cameras.  Both my 24-70, and my 24-105 had the issue shortly after I started using the EOS mirrorless cameras.  Good luck!

Hi JAYSTATON.  I'm having similar problem.  I purchased a Canon EOS R6 just over a year ago & initially didn't have any problems with my EF 100-400mm 1:4.5-5.6 L IS lens using my Canon EF-EOS R Mount Adapter.  Then, a few months ago, I started getting error message "Err 01: Communication between the devices is faulty. Check the camera, lens, or mount adapter contacts."  Initially Err 01 went away after I turner the camera power switch off, then on. Now Err 01 appears immediately I turn the camera on with my 100-400 lens.  I cleaned mount & lens contacts with isopropyl alcohol - still get Err 01.  Two days ago I even updated the EOS R6 firmware to the latest version 1.8.1 per B&H Photo recommendation - still get Err 01.  What do you suggest I do to fix this problem.  Do you still think the issue is with EOS cameras?  Have you heard if Canon has done anything about this issue?  Very frustrated.

If anyone else is having this issue, please chime in.

Thank you.

P.S. When I change lens to my Canon EF 28-135mm 1:3.5-5.6 IS, I don't get the Err 01 message - no problems at all, which suggests the problem is my Canon EF 100-400mm 1:4.5-5.6 L IS lens.

I bet it just hasn't broken yet.  Good luck with it.

Hi cc23.  I am no longer using Canon zoom lenses(except for the 70-200, f4).  I switched to a Tamron 24-70, 2.8, with IS.  It is heavier, but sharper than the Canon.  I had both my Canon zoom lenses fixed and sold them.   A side note: does your ISO sometimes switch to AUTO?  Mine does.  I have to set the max ISO low to prevent it from switching to AUTO ISO and messing up my beach sunset portraits.  I haven't heard of any reason for either issue.  But I still love my Canon mirrorless cameras. 

Canon LIVE! Canon LIVE!