Look in your car owner's manual to determine whether the engine should be on or off when checking the ATF. On most cars, the engine must be fully warmed up and running. On some, however, the engine should be warm but turned off.
 

Open the hood and locate the ATF dipstick at the back of the engine, on the opposite side of the belts. The top of the dipstick may be labeled.
 

Pull out the dipstick and wipe it clean with a rag.
 

Put the dipstick back in the hole. Make sure you push it all the way back in.
 

Pull out the dipstick and check the fluid level. All ATF dipsticks have lines indicating full and low levels.
 

Pour the ATF into the dipstick hole if the level is low. Use a long, thin funnel and add 1/4 qt. (250 ml) at a time if the level is not at the full line. Check the fluid level each time to avoid overfilling.
 

Push the dipstick back into the hole and close the hood.
 

Service your transmission every 24,000 miles (40,000 km) or every two years, whichever comes first. A transmission service includes replacing the filter, draining and replacing the ATF, and replacing the transmission-pan gasket. This service is not part of a regular tune-up; you must specifically ask for it.