Operation Description

WARNING: This page is about a different car, the 2008 Infiniti FX45 and 2008 Infiniti FX35. However, it is still accessible from the selected car via links, so may be relevant.

BCM activates transistors of output terminals (OUTPUT 1-5) periodically, and allows current to flow in turn.
If any (1 or more) switches are turned ON, circuit of output terminals (OUTPUT 1-5) and input terminals (INPUT 1-5) becomes active.
At this time, transistors of output terminals (OUTPUT 1-5) are activated to allow current to flow. When voltage of input terminals (INPUT 1-5) corresponding to that switch changes, interface in BCM detects voltage change, and BCM determines that switch is ON.

Fig 1: Operation Diagram For BCM And Combination Switches

Courtesy of NISSAN MOTOR CO., U.S.A.