Possible reasons:
Transmission Fluid (TF) Problems
*Low TF level
*TF pollution
* TF quality deterioration due to aging
Mechanical faults:
* Worn or broken clutches
* Faulty sensors or solenoids
* Torque converter problems
* Gearbox malfunction
Electrical faults:
* Problems with the transmission control module (TCM)
* Damage to wiring
Other possible factors:
* Worn engine or transmission mount (causes vibration and jerking)
* Engine problems affecting torque (such as spark plugs not working)
*Powertrain Control Module (PCM) malfunction
Diagnosis and elimination:
1. Checking TF level and quality: Make sure the TF level is normal and the TF is pure and red in color. Replace TF if necessary.
2. Scan Trouble Codes: Connect an OBD2 scanner to check for transmission related trouble codes. This can help diagnose certain problems.
3. Physical Inspection: Inspect the transmission and transmission lines for leaks, damage, or loose connections.
4. Check Electrical Components: Use a multimeter or oscilloscope to check sensors, solenoids and wiring.
5. Repair or replacement: Depending on the identified cause, the problematic components may need to be repaired or replaced.
6. Adaptations and Adjustments: After some components have been replaced or repaired, the TCM may need to be adapted or adjusted to ensure proper transmission operation.
Note: It is important to contact a qualified mechanic to accurately diagnose and repair the automatic transmission. Attempting to repair it yourself can make the problem worse and lead to costly consequences.