To diagnose an automatic transmission problem, check the level of the transmission fluid to make sure the vehicle is not losing fluid, check the transmission system for leaks, and check the transmission filter to make sure it isn't clogged. If there are no problems in any of these areas, it is likely that the transmission needs rebuilding.
The first thing to check when diagnosing automatic transmission problems is the transmission fluid. A low level of fluid can cause difficulty when the vehicle is trying to shift gears and can lead to severe damage in the transmission. Make sure the transmission fluid is checked regularly and if it seems to be losing fluid at a rapid pace, there may be a leak in the system.
There are several places to check for a leak in the transmission system. Check the filler tube base, the drain hole underneath the transmission, below the transmission and the engine, the selector shaft which connects the gear shift to the transmission, the speed sensor mounting point, and the radiator.
If there is no leak in the transmission system, check the filter to make sure it isn't clogged. If any debris or clog is found, remove it from the filter. Replacing the filter can also help to solve automatic transmission problems.