What does U0073 mean?

U0073 means a communication bus turned itself off. The network segment that lets your engine, transmission, ABS, body, and cluster modules talk stopped carrying traffic, so the modules on it vanish from the scan tool together and the dash lights up with warnings from systems that have simply lost their data source. This is one of the clearest cases where the number of codes tells you nothing about the size of the repair. A dead bus knocks several modules offline at the same time, and the underlying fault is nearly always singular and shared. Shorted bus wiring is the classic finding: the two CAN wires chafed together, or one of them shorted to power or ground, which forces the network into a protective off state. The second pattern is one failed or shorted module pulling the whole bus down — the network is fine, but one participant is jamming it. Low battery voltage, a corroded ground, and a damaged connector round out the everyday causes, and a gateway fault sits at the very end of the list. Because of that, the job is detective work, not parts replacement. Test the battery and charging system first, then scan every module and write down which ones are missing — the pattern of what is offline tells you which segment you are on. Inspect the bus wiring along its route for chafe points, crush damage, rodent damage, and repairs from past work, and check the connectors and grounds shared by the missing modules. Where it is safe to do so, disconnecting suspect modules one at a time will reveal the culprit when the bus comes back to life. Replacing modules at random is the most expensive way to fix this code and often fixes nothing, because one shorted wire or one bad module can take the whole bus down. Find the fault before anyone quotes you a computer, and expect any genuine module or gateway replacement to need shop or dealer programming.