The main reasons why an automatic transmission can only go backwards:
* Control system failure:
*Faulty Transmission Control Module (TCM)
* Damaged wiring harness
* Faulty shift position sensor
* Mechanical problems:
*Broken forward drum
* Worn or broken friction discs
* Torque converter slippage
* Faulty oil pump
*Hydraulic problems:
* Blockage of hydraulic channels
* Faulty shift valve
* Low automatic transmission fluid level
* Electrical problems:
* Faulty shift solenoid
* Short circuits or breaks in wiring
Diagnostics:
* Visual inspection of automatic transmission
* Reading trouble codes using OBDII scanner
* Dynamic test of road conditions (test drive)
* Hydraulic testing of automatic transmission
Repair:
*Depending on the cause of the problem, repairs may include:
* Replacement of TCM or wiring harness
* Automatic transmission overhaul or replacement
* Cleaning hydraulic channels
* Replacement of solenoids or gear shift valves
* Repair or replacement of torque converter
Note: It is not recommended to operate the vehicle with the automatic transmission only moving in reverse, as this may cause further damage to the transmission. It is recommended to immediately take the car to a car service center for diagnostics and repairs.