"Mechanical diode", one way clutch. Three different names, sprag, roller clutch, mechanical diode. The easiest way to understand this is a bicycle. When you pedal forward, the one way clutch engages and turns the wheel, when you stop pedaling, the wheel continues to turn without the pedals turning. That is a one way clutch. 1st, 2nd and 3rd all have one way clutches operating in this transmission. There are 2 for 1st, 2 for 2nd and 1 for 3rd in operation. Add that up and you get 5 but there is actually only 3 in the trans. Some are used in multiple gears.
Did I mention it also has 5 clutch packs, a band and 4 valve bodies?
Loss of the intermediate mechanical diode will cause a loss of 2nd gear, not 3rd. Preston