There are a few things that can cause this. First, plugged cooler lines from the transmission to the cooler, which usually is built into the radiator, or mounted in front of it. Second, plugged transmission cooler. Third, plugged filter in the transmission. Fourth, overloading the transmission. Fifth, if the cooler is in the radiator tank, and the engine is running too hot, it will also prevent it from cooling the transmission.
It means that your transmission has been hot and the fluid has overheated. If the transmission is still functioning properly then have the fluid and filter changed ASAP.
If your car running less then 10 minutes then it's considered a car with cold transmission fluid (fluid should be in the region of cold level marks, but not lower), if more then 10 minutes then it's hot (fluid should be in the region of hot level marks, but not higher). When you check transmission fluid level your car should be running.
It will tell you on the stick, either "check hot" or "check cold", running or not.
You check the transmission fluid when its hot
Transmission fluid will show full when it is cold, but low when it is hot if it is low on fluid. Transmission fluid has to be checked when the car is warm.
It means the transmission overheated. Have the fluid changed and you may be ok. Then find out why it got too hot.
The first thing to check is transmission fluid level. Start the car and let it warm up to normal running temperature. With the engine still running, pull the dipstick for the transmission fluid and verify that it's in the "hot" range. If you are low on fluid, look for any transmission fluid leaks. Look primarily around the oil seals where the axel enters the transmission, and inspect the gasket for the transmission pan.
Normally your dipstick has a hot and cold mark on it. If not check it hot, always check it with the engine running on an even surface.
Assuming you have the auto transmission and not manual, there's a transmission dipstick near the firewall. Pull that stick and follow the instructions that are inscribed on it. Most manufacturers want the transmission totally up to temperature (hot) and the engine running while checking the fluid level. Cheers
Check engine oil when you have just finished driving. Check Transmission fluid when the car is running and the transmission in in N (manual) or P (automatic).
put tranny in park. make sure its hot and check fluid while egne is running. should be in the cross hatch section on the dip stick.
Add it the same place you check it, through the dipstick tube. Check the level with the transmission hot, in park, engine running, on level ground. Use only Dexron fluid. Do not overfill!!!!!