Possible reasons:
1. Torque converter malfunction:
* Clogged torque converter filters
* Worn or damaged friction discs
* Faulty pressure regulator
2. Transmission problems:
* Worn or damaged gears
* Faulty solenoids
* Insufficient transmission fluid level
3. Malfunction of the electronic control unit (ECU):
* Incorrect signals from sensors
*Software bugs
4. Problems with wiring and connectors:
* Damaged or loose wiring
* Corrosion of connectors
5. Faulty sensors:
*Speed sensor
* Throttle Position Sensor
*Transmission fluid temperature sensor
Diagnosis steps:
1. Check the transmission fluid level and condition.
2. Run diagnostics using an OBD-II scanner to check for trouble codes.
3. Check the torque converter and transmission for damage, wear, or leaks.
4. Check engine and transmission wiring, connectors and sensors.
5. Consult a qualified mechanic for further diagnosis and repair.
Notes:
* Ignoring this symptom may result in serious damage to the automatic transmission.
*Repairs may require special tools and skills, so it is recommended that you contact a professional.
*Repair costs may vary depending on the severity of the problem and the type of vehicle.