OBD-II code family
Vehicle Communication Bus A Faults (2 codes)
2 related fault descriptions. Use each full code and the exact vehicle service information to identify its circuit, monitored condition, and required tests.
Codes in this family
This is the complete published member list for this guide. Each code retains its own page; shared diagnostic context does not mean that every member has the same test or repair.
What these codes mean
U0028 names Vehicle Communication Bus A; U0029 adds Performance. Neither code means Bus B. The exact monitored condition comes from the reporting module’s DTC procedure; a performance label alone does not prove an intermittent wire, failed gateway, or bad controller.
Start with a saved full scan and the exact vehicle network diagram. Establish which systems use Bus A, the supported module list, power and ground supplies, gateway path, and required test conditions. The label does not prescribe a bus technology, speed, topology, or resistance value.
An unreachable group of modules can point toward a shared circuit or gateway path but cannot by itself locate the fault. Use the specified circuit tests before replacing anything. Judge driving safety from actual symptoms and owner guidance; this is not inherently a comfort-only network.
Identify the circuit on your vehicle
Match the full DTC, reporting module, and any failure-type suffix to the service information for your exact year, make, model, engine, and equipment. An identifier alone does not establish installed hardware count, location, connector pinout, or a universal measurement.
Where the manufacturer publishes its own meaning for this code, that is the one to work from — it describes the actual component on your vehicle, which the generic definition cannot. Keep the generic description for what it is good for: it tells you which subject area the standard assigned the code to, which is useful context when the two appear to disagree. If they do disagree, follow the manufacturer.