Some tips to start troubleshooting an automatic transmission is to determine if the fluid levels are correct, if there is a leak or if the filter has a clog. If the problem is too severe, a new or rebuilt transmission may be necessary.
A car owner should check the transmission fluid about two times a year. If the fluid is low, it can cause the car to shift improperly, and it can damage the transmission. If the car is losing a lot of fluid, it's possible that there is a leak. It is fairly easy to check for a leak in the transmission, as there are only a few places in the system where a leak may appear. These areas include at the base of the filler tube, at the drain hole under the transmission, between the engine and the transmission, and at the point where the speed sensor sits.
It is also possible that the filter has a clog. The filter is vital to the transmission's performance, and if the filter is old, a vehicle owner should check this before attempting an expensive repair. Most transmission issues are difficult to repair and require professional assistance. There are many special tools that are necessary, and the repairs require skills that the average at-home mechanic does not have.