Mechanical faults:
* Wear of friction linings or clutch discs
* Damage to planetary gears or shafts
* Malfunctions of the hydraulic unit (valves or solenoids)
*Leaking or contaminated transmission fluid
*Transmission fluid pump malfunction
Electrical faults:
* Faulty speed sensors (input or output)
* Malfunction of the throttle position sensor
* Pressure sensor malfunction
*Transmission control module (TCM) malfunction
*Wiring harness fault
External factors:
* Transmission overheating (due to overload, slipping or insufficient cooling)
*Low transmission fluid level
* Transmission fluid contamination
* Using the wrong transmission fluid
Other reasons:
* Improper repair or maintenance
* Use of non-original spare parts
* Fatigue or over-life of transmission components