Possible reasons:
Torque converter lockup problems:
*Faulty or sticking torque converter lock-up solenoid
* Contaminated or low level automatic transmission oil causing insufficient pressure
Problems with the hydraulic system:
* Low automatic transmission oil pressure due to a faulty pump or valve
* Dirty or clogged hydraulic filter
*Leaking seals or hoses
Mechanical problems:
* Wear or damage to parts in the automatic transmission, such as clutches, drums or planetary gears
Electrical system problems:
* Faulty automatic transmission selector position sensor
*Damaged or loose wiring
Solution:
1. Check the level and condition of the automatic transmission oil: Make sure that the oil level is within the permissible range and that the oil is clean and does not have a burning smell. If necessary, add or change oil.
2. Scan your vehicle for trouble codes: Using an OBD-II scanner can reveal trouble codes related to the automatic transmission.
3. Check torque converter lockup solenoid operation: Use a scan tool or multimeter to check its resistance and operation.
4. Check hydraulic pressure: Connect a pressure gauge to the automatic transmission pressure port and check the pressure at start-up and in various driving modes.
5. Check the hydraulic filter: Remove and check the filter for blockage or damage.
6. Contact a Professional Mechanic: If you are unable to identify and fix the problem yourself, contact a qualified mechanic for further diagnosis and repair.