Possible reasons:
*Low transmission fluid level: Check fluid level and add fluid if necessary.
* Dirty or old transmission fluid: Replace fluid and filter according to manufacturer’s recommendations.
* Worn or damaged bands or clutches: Replace worn parts.
*Damaged torque converter: This can cause loss of transmission fluid pressure. Replace or repair the damaged component.
*Faulty Solenoid: Check and replace faulty solenoids that control gear shifting.
* Electrical faults: Check wiring harnesses, sensors and ECU for faults.
* Faulty Speed Sensor: Incorrect speed readings can interfere with gear shifting. Replace the faulty sensor.
* Software faults: Update or reprogram the transmission control module.
Diagnostics and repair:
1. Check transmission fluid: Check the fluid level and condition.
2. Check Trouble Codes: Use a scan tool to read diagnostic codes related to the transmission.
3. Take it for a test drive: Pay attention to symptoms of slipping, such as floating or lagging gear changes.
4. Check fluid pressure: Use a pressure gauge to measure transmission fluid pressure.
5. Disassemble the transmission: If other diagnostic methods are unsuccessful, it may be necessary to disassemble the transmission to inspect internal components.
6. Replace faulty parts: Replace any worn, damaged or faulty parts identified during diagnosis.
7. Clean and Reassemble: Clean all components and reassemble the transmission.
8. Replace transmission fluid: Fill the transmission with new transmission fluid.
9. Reset adaptive values: If the transmission has been reprogrammed, reset the adaptive values using a scan tool.
Warning: Shifting the transmission requires special knowledge and equipment. If you don’t have experience repairing transmissions, it’s best to seek help from a qualified mechanic.