why do you have to have to car running in order to check or to fill the transmission up with fluid. Why can’t you just check the fluid like you would oil.
To check it with the engine NOT RUNNING would give and inaccurate reading. The torq converter has to fill with fluid, and the fluid has to be WARM at least to get an accurate reading. That’s just the way it is. I can also tell you why the sky is blue, but the chemical explanation is rather long.
Some vehicles are checked without the engine running. Proper methods are different for different vehicles.