Thomas school buses along with Freightliner highway trucks have multiplexing software built in to reduce wiring and connections. It’s similar to optic cable where messages are flying back and forth at high speed. To make all of this work there are several modules that interconnect with J1939 to relay inputs and outputs. if the operator wants to use a heater motor when the switch is activated it sends a message from the switch hub module to the bulkhead module and it relays a command to the appropriate heater motor according to the resistance in the switch. Each switch resistance level indicates what it runs.
This happens at high speed and works very well. If there is an issue the Diagnostic Link 8 software is the best tool to have… as seen in the video you can activate a circuit starting at the BHM which is the brains of the system. From the BHM everything connects to make a circuit happen. With the software you can detect where there may be a problem along the way. An open circuit or corroded wire will show up in the diagnostics. When activating one of the circuits which in this case is the windshield washer pump there was a graph showing the amperage draw. This is quite useful in determining if the pump is not working which will be of course a flatline pattern.
The only way to get proficient at this software is to play with it. It’s extremely rewarding to find an electrical problem using modern technology instead of the old school method of hunting down wiring and standing on your head. Once you get a feel for the program it just gets easier. Let me see… just like riding a two wheeler bike. Once you find out how to keep it straight and mobile it’s easy sailing. I’ve been in this trade for 41 years and every day is a learning experience. Don’t ever tell yourself you know everything.
All I know is the troubleshooting part is the best part and having the engine software in hand multiplies the chances of zeroing in on the problem. In fact if you are working on any diesel 2007 and newer you must get the engine software or you’re sunk before even getting in the boat. I hope to publish more of these demo type videos and repair/maintenance videos as the problems occur. I can’t predict what the next repair will be but that’s what makes this job so damn interesting.