Possible reasons why the automatic transmission only goes in reverse:
1. Problems with the gear selector:
* Faulty gear selector that does not shift the transmission into forward mode.
*Damaged or loose selector cable.
2. Problems with the transmission control module (TCM):
* Faulty TCM that does not control transmissions properly.
* Damaged wiring or connections to the TCM.
3. Problems with gear shift solenoids:
* Faulty shift solenoid that does not engage to shift into forward gear.
* Dirty or clogged transmission fluid passages preventing solenoids from operating.
4. Problems with planetary gear:
* Damaged or worn planetary gearbox that is not transferring power to the forward gears.
* Faulty planetary gear bearing causing seizure or slippage.
5. Problems with the hydraulic system:
*Low transmission fluid level or leak causing insufficient hydraulic pressure.
* Clogged or dirty transmission filter restricting fluid flow.
6. Other reasons:
* Damaged wiring or connections to the automatic transmission.
* Faulty sensors such as the throttle position sensor or RPM sensor that provide incorrect information to the TCM.
What to do:
1. Check the transmission fluid level and add it if necessary.
2. Inspect the gear selector and cables for damage.
3. Take the vehicle to a service center for diagnostics, which may include:
* Scan fault codes
* Checking the hydraulic system
* Disassembly and inspection of automatic transmission