I think he meant pull the fill plug, and either fill (if under filled) or drain (if over filled) through the fill plug.

The X definitely needs to be started or you will lose a lot of fluid out of the fill plug. I only know the procedure for the ZF trans, but assume the GM trans is similar. Must be filled warm and running. Final fill between 40c and 50c. Again, that's ZF trans. Have no experience with the GM trans.

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