Possible reasons for an automatic transmission slipping in 4th gear:
Mechanical problems:
* Wear of friction discs and steel plates
* Torque converter malfunction
* Problems with the oil pump
* Clogged oil filter
* Wear of O-rings and gaskets
Hydraulic problems:
*Low transmission fluid level
* Insufficient fluid pressure
* Shift solenoid malfunction
* Clogged or leaking hydraulic control system
Electrical problems:
*Speed sensor malfunction
*Transmission control module (TCM) malfunction
Other reasons:
* Excess weight in the car
* Aggressive driving style
* Towing heavy loads
Diagnostics:
To diagnose the exact cause of slipping, you must do the following:
* Inspection of the level and condition of the transmission fluid
* Reading and decoding fault codes using a scanner
* Testing fluid pressure in automatic transmission
* Visual inspection of friction discs and steel plates
* Checking solenoids and sensors
Troubleshooting:
Depending on the cause of the slippage, the following repair work may be required:
* Replacement of friction discs and steel plates
* Repair or replacement of torque converter
* Repair or replacement of oil pump
* Replacement of oil filter
* eliminating leaks and replacing o-rings
* Filling or replacing transmission fluid
*Increasing fluid pressure
* Replacement of gear shift solenoid
* TCM repair or replacement
*Adjust TCM parameters
*Modification to increase transmission strength (in case of excessive load or aggressive driving)
Recommendations:
* Check the level and condition of the transmission fluid regularly.
* Avoid sudden acceleration and gear changes.
* Do not overload the vehicle.
* Perform routine maintenance, including changing the automatic transmission fluid and oil filter.