I have a EF 100-400 f 4.5-5.6 l series lens. It is suddenly having a hard time communicating with the camera. I get an error message that says clean the contacts, which I have done. The problem persists. I am in Panama, and there is an authorized Canon service center, but I would like to know if there is any further trouble shooting I can do at the house without taking it to the service center 6 hours away.
Are you using it with an extender or just by itself?
With an extender, you should mount the extender to the lens first before mounting on the camera, otherwise you might get this error a lot.
Besides cleaning the contacts (which rarely works) and power the camera off, removing the battery and wait a while for total discharge, there's not a lot of things you can do.