Possible reasons why the Kia Sportage automatic transmission only works in 4th gear:
1. Transmission problems:
* Shift control solenoid malfunction
* Wear of clutches or steel discs
* Transmission fluid leaks
* Malfunction of the electronic transmission control unit (TCU)
2. Electrical problems:
* Open or short circuit in the wiring leading to the transmission
*Speed sensor malfunction
* Faulty gear selector position sensor
3. Hydraulic problems:
*Low transmission fluid level
*Transmission filter clogged
* Air in the hydraulic system
4. Other mechanical problems:
* Worn input shaft or gear
*Differential fault
* Shift or damage to internal transmission components
Steps to diagnose and fix the problem:
1. Check the level and condition of the transmission fluid.
2. Scan the vehicle for fault codes.
3. Check wiring for breaks or shorts.
4. If necessary, replace faulty sensors or solenoids.
5. Flush or replace the transmission fluid and filter.
6. Bleed the hydraulic system.
7. If the problem persists, contact a qualified mechanic for further diagnosis and repair.
Note: Ignoring this problem can result in severe transmission damage and costly repairs.