Where is the ecm?

Sorry for the total noob question but I need to know where the ecm is located on my 04 Chevy Avalanch.

ECM (Electronic control module) is located behind the radiator, just below the battery and the underhood fuseblock.  Has plastic shroud and two rows of wires in the connectors.  BCM (Body control module) is located behind the dash panel under the steering wheel.

Thank you very much for the help.

FYI, that's the PCM. in that box below the battery area. The Emission Control Module is integrated within it.

Names and assignments vary between brands and models of course, so it's easy to refer to other common configurations.

All emission DTC's store or "report" from the PCM in GMT800 vehicles.