when the engine is shutoff half of the torque converter drains back to the pan due to gravity, if the pump is not working or the flexplate has broken or the bolts holding the torque converter have sheared off (they are mandatory to renew every time they are disturbed) the transmission will not work as the main pump doesnt work.

You will also see a high level on the dipstick. To test follow was ps2cho said, undo a cooler line and see if you get any fluid pumping from it as soon as the engine starts.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)