Possible reasons why the automatic transmission only works in 1st gear:
Transmission problems:
* Faulty shift solenoid
* Slipping or burnt friction clutch
* Broken drive shaft
* Worn rings and pistons
Problems with the control system:
* Faulty speed sensor
* Faulty Transmission Control Module (TCM)
* Open circuit or short circuit in electrical wiring
Low transmission fluid level:
*Low fluid level may cause insufficient pressure to shift gears
Other possible reasons:
* Stuck mechanical link
* Shifting the gear lever to position ‘L’ or ‘1’
* Emergency mode enabled due to other problems
Diagnostics and repair:
* Diagnostics using trouble code scanner (OBD2) to detect transmission fault codes
* Checking the level and condition of the transmission fluid
* Visual inspection of mechanical and electrical components
* Repair or replace faulty components such as solenoids, clutches and sensors
Note:
If you notice any of these problems, it is important to seek help from a qualified mechanic immediately. Continuing to drive with a faulty automatic transmission can result in more serious damage and costly repairs.