Possible reasons:
1. Gearbox malfunction:
* Wear of clutch discs or clutches
* Torque converter malfunction
* Contaminated or low transmission fluid (ATF) level
2. Sensors:
* Faulty input/output speed sensor
* Faulty ATF temperature sensor
3. Electrical faults:
* Short circuit or break in wiring
* Faulty Transmission Control Unit (TCU)
4. Other:
* ATF cooler blocking
* Insufficient transmission cooling due to poor ventilation or dirty fan
* Too low or high ATF pressure
* Worn or damaged oil pump
Diagnostics:
1. Check ATF level and condition.
2. Connect an OBD2 scanner to search for trouble codes.
3. Check the ATF speed and temperature sensors.
4. Inspect the electrical wiring for damage.
5. Make sure the ATF cooler is not blocked.
6. Check ATF pressure and condition of the oil pump.
Potential solutions:
* Replacement of faulty gearbox parts
* Installation of a new torque converter
* Replacing or topping up ATF
* Replacement of faulty sensors
* Correction of electrical faults
* Cleaning the ATF cooling radiator
* Improved gearbox ventilation
* ATF pressure adjustment
* Replacement of oil pump