Databus communication errors are typically not something the average person can properly troubleshoot. Key off, you should see about 60 ohms between the high and low wires. Typically a range of 55 to 65 ohms is acceptable. If its just one module (ECM) not communicating, chances are its in that particular leg of the datalink. Could be a broken datalink wire, no power to the module or a broken ground from the module. Could be the module itself failed but its unlikely an ECM has failed. They're pretty bulletproof for the most part.
