i have a problem that the four wheel is always connected! how can i fix it ? or what is the problem?

Do you have manual or electric shift?

electric shift

Perhaps the shift motor is not working. I would first check fuses and relays but you may need to replace the shift motor. You could remove it and see if it works when not attached to the transfer case. You could also check to see if the motor is getting power. If you have been driving a long time with the car in 4WD the transfer case may be damaged.

i did scanner but nothing appears ..

the shift motor is a mechanical part or electricity part ?

The shift motor uses electrical power to shift the transfer case in and out of 4WD.

The electrician who checked the four-wheel drive did not find a problem in it and the key changed the slow and fast 4WD works good

Then why do you say it is stuck in 4WD?

beacuse when i want to drive and turn the wheel right or left the wheels stuck and don't walk easily

Do you have it set to 2WD? Did the mechanic verify that it was shifting into 2WD? Also have him check the front hub locks.

i have on the switch key neutral or automatic or fast or slow

usually it is 2wd but when there is snow or oil on the road it change automatically to 4wd

If the shift motor works and the automatic hubs work then your T-case is bad.