Possible reasons:
Problems with automatic transmission fluid:
*Low fluid level
* Contaminated or not changed fluid for a long time
* Incorrect viscosity or fluid type
Problems with the mechanical part of the automatic transmission:
* Wear of friction discs
* Dirty or faulty solenoids
* Torque converter problems
* Wear of bearings and gears
Electronic problems:
* Faulty automatic transmission speed sensor
* Faulty torque converter lock-up solenoid
* Problems with the automatic transmission control unit (TCM)
Other possible reasons:
*Low engine oil pressure
* Malfunction of the automatic transmission oil pump
* Burnt electrical wire
Troubleshooting steps:
1. Check the level and condition of the automatic transmission fluid.
2. Replace the automatic transmission fluid and filter. Use the correct fluid type and viscosity recommended by the manufacturer.
3. Inspect the mechanical part of the automatic transmission. Check for wear or damage on friction plates, solenoids, torque converter and other components.
4. Conduct diagnostics of the automatic transmission electronic systems. Use an OBD2 scanner or a dedicated automatic transmission diagnostic tool to check for trouble codes and system parameters.
5. Check engine oil pressure. Low oil pressure can lead to problems with the automatic transmission.
6. Check the automatic transmission oil pump. A faulty pump may not provide enough pressure to operate the automatic transmission.
7. Check the automatic transmission wiring. A burnt or damaged electrical wire can disrupt the operation of electronic systems.
Note: Troubleshooting automatic transmissions can be complex. If you do not have the appropriate skills or tools, it is recommended that you seek assistance from a qualified mechanic.