Possible reasons:
Mechanical problems:
*Low or contaminated transmission fluid (ATF)
* Slippage or wear of automatic transmission clutches
* Torque converter malfunction
*Damage to planetary gear
Electronic problems:
* Faulty gear shift solenoids
* Problem with electrical wiring (breaks, short circuits)
* Faulty gear selector position sensor
* Failure in the automatic transmission control unit (TCM)
Troubleshooting steps:
1. Check the ATF level and condition: A clean and sufficient fluid level is necessary for proper lubrication and operation of the automatic transmission.
2. Scanner Diagnostics: Connect a scanner to the vehicle’s diagnostic port to read trouble codes that may indicate specific problems.
3. Reset adaptations: The automatic transmission can adapt to the driving style. Resetting adaptations can eliminate problems caused by incorrect adaptations.
4. Check Shift Solenoids: Faulty solenoids can cause problems when shifting gears. They must be checked using a scanner or ohmmeter.
5. Electrical wiring inspection: Check the automatic transmission wiring for damage, breaks or short circuits.
6. Shift Position Sensor Replacement: A faulty sensor may produce incorrect signals to the TCM, resulting in incorrect shifts.
7. TCM Replacement: The automatic transmission control module may become faulty and cause various shifting problems.
8. Overhaul of automatic transmission: In severe cases, overhaul or replacement of the automatic transmission may be required.
Important: It is not recommended to continue driving a car with a faulty automatic transmission, as this can lead to serious damage to the transmission. Contact an experienced mechanic for diagnosis and repair.