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NO! There are numerous locations where grounds are located! The PCM is actually grounded in more than one location. Here is a post that I started a while back that has a lot of electrical info and a list of ground locations.
I am not really having problems, I am finishing up the install of my LM-1 wideband O2 reader with accessory signal recorder. I would like to record the MAP and IAT signals. The accessory reader needs to be grounded to the same ground point as the sensors or as close as possible. I assume that all the sensors where grounded through the PCM and it was grounded in a single location.