Vehicle architectures may use standalone or integrated gateway functions to manage communication between network segments. The underlying buses, routing behavior, and gateway topology vary by manufacturer and platform. Receiving modules monitor incoming network frames across connected bus segments; code U0146 sets when expected gateway status messages or routed cross-bus data frames remain absent over designated monitoring evaluation intervals according to the vehicle's network-supervision strategy. Note that malformed or invalid-data faults belong to different DTC families and should not automatically be treated as the same condition as lost communication.