Shift solenoid: The shift solenoid controls the engagement and disengagement of gears. A faulty solenoid can cause the transmission to not shift properly.
Transmission control module (TCM): The TCM is the computer that controls the transmission. A faulty TCM can cause a variety of transmission problems, including not shifting properly.
Torque converter: The torque converter is responsible for transferring power from the engine to the transmission. A faulty torque converter can prevent the transmission from engaging properly.
Mechanical problems: There may be a mechanical problem with the transmission itself, such as a broken gear or a damaged synchronizer.
