change oil sending unit on a 2003 envoy on 2003 GMC Envoy

the oil gauge goes from 80 to 0 back to 80 no engine noise like if there was low oil level and check engine turns on then a turn engine off warning then it all disappears.
My scanner does not read any codes?
I'm planning to change the oil sending unit and need to know where it is and how to do it.

Asked by for the 2003 GMC Envoy