Possible reasons:
1. Low transmission fluid level
* Check the fluid level and add if necessary.
2. Contaminated or old transmission fluid
*Change transmission fluid regularly according to manufacturer’s recommendations.
3. Dirty or faulty transmission filter
* Replace filter and fluid.
4. Faulty shift solenoid
* Solenoids control the flow of fluid to the transmission. Faulty solenoids can cause shifting problems.
5. Valve body malfunction
* The valve body controls the fluid flow in the transmission. A faulty valve body can cause shifting problems.
6. Speed sensor malfunction
* The speed sensor tells the transmission about the vehicle’s speed. A faulty sensor can cause gear shifting problems.
7. Electrical problems
* Check all electrical connections in the transmission and make sure they are secure. Loose or damaged connections can affect transmission performance.
8. Engine problems
*In some cases, engine problems, such as low fuel pressure or faulty spark plugs, can cause the engine to stall when shifting into gear.
9. Dirty throttle valve
* A dirty throttle valve can interfere with normal engine operation and cause the engine to stall when the vehicle is in gear.
10. Transmission control module (TCM) malfunction
* The TCM controls the operation of the transmission. A faulty TCM can cause shifting problems.
Recommendations:
* Check the level and condition of the transmission fluid.
* Inspect and replace the transmission filter.
* Scan your vehicle for trouble codes.
*Consult a qualified mechanic for diagnosis and repair.