School Bus Multiplexing

imported_John Whelan - November 8, 2015
Since multiplexing is a main stay in highway trucks I want to go through it in more detail so if you're a mechanic in the multiplexing world you will see more of the benefits that this new type of wiring communication system brings. The video was a quick view of what smart switches look like and a typical wiring schematic showing the switch hub module that communicates using inputs and outputs from the smart switches and then to the bulk head module.

What are the Benefits of Multiplexing?

For mechanics the benefits of multiplexing really helps out with troubleshooting and repair. I have to admit this system was intimidating at first just wrapping your brain around it and working with this type of technology. If you haven't got the accessfreightliner link on your laptop along with a user and password you will definitely need it when working on any truck made by Freightliner.

One of the main benefits of multiplexing is the 40% reduction in the amount of wiring in the C2 Saf-t-liner conventional school bus. This is 650 wires down to 350 which translates into three hundred fewer failure areas. The diagnostic side is more efficient with an onboard computer that picks up fault data that sends messages to the instrument cluster in the dash that lets the driver know something is not right.

'Servicelink' is Mechanic's Best Friend

Another avenue to take for multiplexing faults is 'Servicelink' that is part of the accessfreightliner website. Once you log in and get into 'Servicelink' you can view endless information on faults, module templates, configurations and features in each module. The mechanic can easily view each circuit according to module connectors and pins and see what the battery voltage is reading and what each circuit is drawing in amperes.

The test mode when you're in a module template lets you turn on each circuit to see if it's communicating properly. In other words you're checking the outputs and inputs. The hard wiring has also been changed with color code and numbering which is always nice when tracing a circuit. As I mentioned in the video the smart switch position can be changed anywhere on the dashboard if the driver wishes for easier accessibility when driving.

Multiplexing is similar to broadband cable that allows multiple messages to be transmitted just like the internet, TV and telephone. Less relays and connections along with the ability to add a circuit to any module easily makes multiplexing a huge advantage for the end user especially the mechanic who works on these electrical systems. Once you get some hands on experience with multiplexing you'll soon see the benefits.




School Bus