Possible reasons why the automatic transmission stopped shifting:
Mechanical problems:
* Worn or damaged shift solenoids
* Clogged or leaking automatic transmission fluid
* Torque converter problems
* Faulty speed or position sensors
Electrical problems:
* Break or short circuit in the automatic transmission wiring
* Malfunction of the automatic transmission control module (TCM)
* Malfunction of throttle position or mass air flow sensors
Other problems:
* Low automatic transmission fluid level
* Contaminated automatic transmission fluid
* Worn or damaged clutch clutches
* Incorrect automatic transmission installation
Diagnostics and troubleshooting:
1. Check the level and condition of the automatic transmission fluid. Low or dirty fluid can cause shifting problems.
2. Scan the vehicle for fault codes. Error codes may indicate a specific malfunction in the automatic transmission system.
3. Inspect the automatic transmission. Look for fluid leaks, loose connections or damaged components.
4. Check the shift solenoids. A faulty solenoid may not engage or disengage the appropriate gear.
5. Check speed and position sensors. Incorrect sensor readings may result in incorrect gear shifting.
6. Check TCM. The TCM controls gear shifting and a malfunction can lead to shifting problems.
Note: Diagnosing and repairing an automatic transmission requires specialized equipment and knowledge. It is recommended that you contact a qualified mechanic to properly identify and repair the problem.