The BMW E39 belongs to the BMW 5-Series vehicles. The BMW 5-Series transmission includes a dipstick in the engine compartment to simplify the process of monitoring fluids in the transmission. You should check the transmission fluid at every oil change, when you notice hard shifting or your transmission has high miles. BMW recommends using only Dexron III transmission fluid in the 5-Series.
Park the car on a flat surface. Start the engine and turn on the air conditioning. Engage the brake and shift the transmission through each gear, waiting three to five seconds between shifts.
Return the transmission to "Park." Open the bonnet of the car. Pull the transmission dipstick located in the centre of the engine compartment, near the firewall.
Wipe the dipstick with a clean paper towel. Insert it into the tube then promptly remove it. Check the fluid level to confirm that it is low. If the fluid level is at the "Min" line or below, add fluid.
Turn the ignition off. Locate the filler plug on the bottom rear of the transmission. Pull the filler plug straight out of the transmission.
Insert the nozzle of the transmission fluid bottle into the filler hole. Squeeze the bottle to fill the transmission with fluid. Check the dipstick again after adding fluid.
Do not overfill the transmission or serious damage may occur to the gears and seals.