Possible causes and solutions:
1. Low transmission fluid (ATF) level
* Check the fluid level according to the instruction manual.
*Add the same type of liquid as above.
2. Contaminated transmission fluid
*If the fluid is black or smells burnt, it needs to be replaced.
* Drain the old oil and replace it with new oil, including a new filter.
3. Faulty shift solenoid
* Solenoids control gear shifting. A faulty solenoid can cause shifting difficulties.
* Test solenoids and replace faulty ones if necessary.
4. Worn clutch packs
*Clutch packs transfer power from the engine to the transmission. Worn clutches can make shifting difficult.
* Replacing clutch packs requires professional repair.
5. Faulty Transmission Control Module (TCM)
* The TCM controls the operation of the transmission. A faulty TCM can cause difficult shifting.
* Test the TCM and replace it if necessary.
6. Problems with a mechanical component
*A broken check valve spring or clogged oil passage may make shifting difficult.
*Professional repair is required to diagnose and fix these problems.
7. Faulty vehicle speed sensor
* The vehicle speed sensor tells the TCM about wheel speed. A faulty sensor can cause the transmission to malfunction.
* Test the vehicle speed sensor and replace it if necessary.
Important:
*If you have never worked on a transmission before, seek help from a qualified mechanic.
*Do not ignore symptoms of difficult shifting, as this may lead to more serious problems and costly repairs.