Selecting 4 wheel drive on its own.

I drive a 2011 Jimny which has been fine with no problems. Of late when I start up the car from cold it will select 4 wheel drive without me pushing the selector switch. I then have no problems taking it out of 4x4 once I notice the issue and I can select 4x4 when I wish with no problems.
I have checked the wiring underneath to the transfer box with nothing obviuous showing and have looked at the 4x4 stuff in the engine bay again with nothing obvious. I do use 4x4 on a regular basis.
My only conclusion at present is to get a new/second hand switch, so any pointers would be much appreciated.

bryn

Have you gone through it with contact spray for water ingress?

I am a little worried when you say that you have no problem taking it out of 4x4 when you notice the issue. Can you tell us how far you might have driven before you noticed, on what sort of surface you were on at the time and whether you noticed a bang or a shudder when you did switch the 4x4 off.

Roger

It happens a soon as I start the car up. No movement..

Bryn

Has the car had any modifications done? Like electrical in the dash or stereo or central lock or ignition? Anything under the car around the transfer box?
Often strange electric flaws comes from mishaps from fiddling or bad ground.

Also if you can. Disconnect the battery overnight to let it reboot the controller.