Start with the network as a system
A communication fault does not automatically mean the named module has failed. A module can disappear from the network because it lost power or ground, a branch is open or shorted, termination is incorrect, a connector is damaged, or the module itself is not communicating. The diagnostic sequence should separate those possibilities.
Physical-layer checks
With the vehicle in the correct safe state for the test, technicians can use the approved service procedure to evaluate network resistance, CAN-high and CAN-low behavior, shorts to power or ground, connector condition and branch continuity. Resistance and static voltage checks are useful, but they do not by themselves prove that every message is valid on an active network.
Missing heartbeat strategy
Identify exactly which messages or modules are missing and what they have in common. Verify power and ground at the affected module, understand the network topology, determine whether other devices on the same branch are present, and isolate wiring or devices methodically. This is usually more efficient than replacing the module that generated a missing-message fault.
Using CAN-analysis software
CAN tools can capture messages and decoded signals over time. Trending a value, comparing commanded and actual states, or identifying when a heartbeat disappears can connect an intermittent symptom to a specific event. The tool is most effective when the technician already understands the schematic, network path and expected operating state.