24 - 105 F/4L stopped to autofocus

[Kamelot]

Hello members,
yesterday i noticed, that my lens do not autofocus. I started to check my camera settings, but nothing changed.
When i turned off my Image Stabilizer, push shutter button half the way, i heard, that lens tries to autofocus - i hear high frequency sound, but nothing happen within lens.
Finally i detached lens from camera and looked to the contacts. They appeared perfectly clean, because this is my only lens and i do not detach from camera often. I tried to touch contacts with clean and soft napkin, then attached lens to camera and autofocus started to operate.

Now i think, is this a sign, that my lens need service?
Maybe i should send to canon service?
Or is this almost normal, when happens rare?
I have my lens 2,5 year and this is first malfunction.

P.S. Sorry for my not so clear english.

[DavidEccleston]

Another option, because sometimes it's the most obvious things we overlook, the sound you hear isn't the focus motor at all, but the IS unit, and lens just has the auto focus mode switch switched to MF.

[Kamelot]

In the past when removing camera from the camera bag my fingers have wrapped far enough around the body to press the lens unlocking button. Combined with a little twist while removing the camera it has twisted the lens off part way, so no AF or anything.

Possible. Because sometimes i twist Mode dial button. But difference is that my lens Image Stabilizer was operating perfectly. Just autofocus didn't operate.

A second, less likely, cause can be wear or damage to the lens locking pin from the camera body or in the mating groove in the lens.

I can count lens attaching/detaching to camera times. And that number is between 10 to max 20 times per 2,5 years. I think it is really low possibility to damage pins or lens locking mechanism.

Another option, because sometimes it's the most obvious things we overlook, the sound you hear isn't the focus motor at all, but the IS unit, and lens just has the auto focus mode switch switched to MF.

I checked 3 or more times. Tried to switch to MF and again to AF. Result was the same. I recognize the IS sound. I switched off my IS and then tried to listen. When i was pressing the shutter button, i heard very quiet sound, something like high frequency. The sound appeared exact time, when i was pressing the shutter button, but no AF lens moving sound.

Thanks jrw, i will observe my lens/camera locking mechanism.