Possible causes of the problem:
Mechanical:
*Transmission Damage: Worn or broken gears, shafts or clutches can prevent you from shifting to higher speeds.
* Torque Converter Problems: Damaged or leaking hydraulic fluid in the torque converter can result in loss of pressure and inability to shift gears.
* Gear selector problems: A broken or incorrectly adjusted gear selector may cause the transmission to not recognize commands to shift to higher speeds.
Electrical:
* Shift Solenoid Failure: Shift solenoids control the flow of hydraulic fluid to shift gears. Their malfunction may prevent switching to higher speeds.
*Transmission Control Module (TCM) malfunction: The TCM monitors transmission operation and may experience malfunctions that result in limited shifting.
* Harness problems: Damage or corrosion to the wiring harness connecting the TCM to the transmission can disrupt communication and prevent gear shifting.
Other:
*Low Transmission Fluid Level: Low fluid level can cause insufficient pressure and make it difficult to shift gears.
* Contaminated transmission fluid: Contaminated transmission fluid can clog hydraulic systems and prevent smooth shifting.
What to do:
1. Check the level and condition of the transmission fluid.
2. Scan the system for trouble codes.
3. Consult an Experienced Mechanic: Transmission diagnosis and repair requires specialized equipment and knowledge.