[header] How to change transmission fluid [title] Check the level of transmission fluid first using the dipstick. [step] Automatic transmission fluid (atf) is the fluid used in vehicles with self-shifting or automatic transmissions. It's typically colored red or green to distinguish it from motor oil and other fluids in the vehicle. 
On most vehicles, you can check the level with a dipstick, while the engine is running. [substeps] Look for the transmission fluid dipstick, which is usually red-handled.