1. Read your Mercedes owners manual to determine the viscosity of the transmission fluid that you need. Only purchase the type of fluid as recommended in the owners manual. The manual will also indicate if you should add fluid when the vehicle is cold or warm, and where the transmission dipstick is located.
2. Turn the vehicle on, if the owners manual suggests adding fluid when the vehicle is warm. Ensure the vehicle is on an even surface for the best reading result.
3. Open the hood and locate the transmission dipstick. Refer to the owners manual for specific location. Many transmission dipsticks are located at the back of the engine, and they may be labeled.
4. Unscrew the cap, if necessary, and remove the dipstick. Wipe it with a rag or cloth to remove the fluid.
5. Insert the dipstick back into the transmission fluid and then remove it. Hold the stick and look at the fluid level on the stick. The stick will be marked with markings to indicate where the level would be full or low.
6. Place the funnel into the hole and add a small amount of fluid. Wipe the dipstick and insert it back into the hole, then remove it and check the level. Repeat until the dipstick reads at the full level.