Here are some signs that it’s time to flush your transmission: Dark red or brown fluid on your transmission dipstick - Fresh ATF is brilliant red. If the fluid on your dipstick is dark, it means that foreign particles have accumulated in your ATF. Transmission slipping - Poor coordination between the engine and your vehicle. If you hear the engine engage but your vehicle seems to respond out of sync, you could have ineffective ATF or a leak. Shifting feels or sounds different - Both of these problems can indicate ineffective ATF or a leak. Midas visually inspects your transmission fluid as part of every Midas Closer Look Vehicle Check. But between Midas visits, any transmission problem should be checked out as soon as possible. Your transmission is one of the costliest parts of your vehicle to replace, so fixing a small transmission problem (while it’s still small) is a big win.