b"NOTEThe acknowledgment bit always has a higher differential voltage amplitude at the end of the data packet due to the electrical loading on the bus when all modules broadcast their ACK bit at once. The amplitude of the ACK bit changes with the number of modules acknowledging any given message.If there is a module hogging the bus, we will generally observe a repeating communication attempt, or a single packet error will often knock out the acknowledgment bit entirely. When we observe this, we want to begin isolating the network using our topology layout and data lines wiring schematic.CAN Nodes with Rogue ElectronsTo start this discussion, let's harken back to where we mentioned how important it is to test the system loaded and live. This is because many module (CAN Node) faults will only occur when operating and pushing current (broadcasting) on the bus.from the bus lines when it senses too many error messages. The transceiver is supposed to de-couple the node from the computer driving it. When this happens, we will see very recognizable waveform characteristics showing that this is occurring. Figure 9 shows one stage of this failure.At this point, multiple DTCs will usually set. But this is where it gets tough to diagnose because the node often doesnt take itself fully off the bus; it electrically hangs. When this happens, the bias voltage becomes pulled down (usually on the LO bus only when node damage), and communication gets scrambled. Figures 9 and 10 nicely capture this. Start node isolation at this point until your bus returns to normal.Power ProblemsStarting with the basics (which is actually where most good techs out-tech themselves), power and ground checks are often needed when diagnosing the network modules. We can also accomplish this task very quickly and accurately by voltage dropping the modules powers and grounds on the lab scope.On that same note, we see a lot of network faults due to battery condition. Were talking main vehicle battery here, and lots of issues with the battery not being registered correctly or at all, so that the energy management system cannot properly charge and maintain it. Believe it or not, battery sensors can wreak havoc with networks too. Any or all of these basic power issues can contribute to the cause of your string of CAN faults. In milliseconds. Literally.We will often ask the technician to rig the scope into the affected network in advance of a cold start, so that we capture all of the wakeup and startup activity on the network on wakeup. This technique often finds the main battery or associated problem at fault, so remember, with cascading codes having to do with over or under voltage conditions, this strategy often bears fruit.10"