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Speedlite 600EXII-RT losing link with Canon transmitter ST-E3-RT.


I've never had a problem with my Speedlite/transmitter until recently.  However, they won't stay linked for more than a few shots. If I turn them both off/on, the link is re-established.

I tried switching ID numbers, switching channels, but the fix is only temporary.

I'm using a Canon 5D Mark III camera.

The battery compartment on the transmitter has a white dot. The flash does not. (I saw this on the Canon site as a possible issue)

Is it possible to update the firmware for the Speedlite? 

Thank you.


Product Expert
Product Expert

Hi there,

There is an updated version of the Speedlite Transmitter ST-E3 RT, and the transmitter itself can be upgraded by the factory service centers. You would initiate that process the same as a repair order, in the service and repair page linked below:


Canon Support | Service & Repair | Canon U.S.A., Inc.


Is there a service charge? I've read others have had this repair without success, is that true?


I sent my 2 ST-E3 RT Transmitters and 4 600 EX-RT Transmitters to have a firmware update as they met the requirements of Serial number range to be updated do to “ Link Drop” located on a Canon site. However only the two transmitters were upgraded as they have the Silver Metallic Sharpie dot applied under battery cover door and the designation of Sender, not Master like before going back to 2012 when first purchased. However the 600’s were not updated as they still have Master and Slave. Why weren’t they updated as requested?

Set up all six pieces and linked only to “ Link Drop” as before which started all of a sudden starting in February 2023. one day in home trying to shoot just one 600 in a Westcott Apollo Orb, without any real change in “Interference” causation. No new routers, Bluetooth Speakers turned off etc. 

Still “Link Drop” occurring consistently here inside, in the back yard and at a neighbors a few houses away. 
Regarding  particular situations in settings, like all good trouble shooting your try every possible scenario, like Channel Scanning and applying strongest, to User ID to only one flash to four flashes, this Transmitter or that one. Transmitter On camera or off camera… a 600 as a Master to emanate if Transmitter is faulty… I know how to trouble shoot.
Canon’s reply…. Interference…… My Reply…. What Interference is causing my old trusty 2011 technology Speedlites to now becoming a fingers crossed unreliable product at a job site? 

As a CPS Gold Member, I have been pursuing this issue and pushing up the chain of command to get this issue identified and solved as that many, many are now having the same issue…Link Drop.