I think the module gets baro. from the MAP sensor at key-on.
This is located next to the fuse box under the steering wheel. It's a matchbox sized black 'L' shaped thing with a three pin connection and it will have a piece of vacuum pipe going from it to the airbox.
Question about that sensor, is it only to show you the underpressure in the air cleaner box displayed now on your dash, or is is also given worthwhile data-input for the ECU, let's say data-input useful for the motor management. Who can tell me more?