5 Multiplexed Electrical System Service Manual Service Resources Communication Diagram Communication diagrams illustrate the signal transmissions between components (switches, sensors, control units, CAN lines, etc.) necessary to perform system functions. Disabled Gauges With the CECU, disabling a component turns the component off completely. The disabled component is removed from all signal transmissions in order to allow the other features on the vehicle faster communication. A disabled gauge will not function or communicate with the control unit.
Controller Area Network (CAN) Communication The following diagram provides an example of the communication lines and signal paths of a typical multiplexed vehicle. Determining the correct communication lines that provide a signal to the CECU and where these circuits interconnect, help pinpoint possible trouble areas. Sometimes these connections become loose, have bent or misaligned pins, and visually inspecting them may help identify why other electrical problems may be occurring. NOTE Check the program menu to see if an inoperative feature is disabled. This is very important when diagnosing an inoperative gauge on a CECU equipped vehicle. The gauge may have been previously disabled.
When a service technician installs an optional gauge in the multiplexed instrumentation system, the newly installed gauge will initially be disabled. Because the gauge is not factory-installed, the technician must program the CECU to monitor it. Until the CECU is programmed, the link between the CECU and the gauge is termed “disabled” that is, the CECU is prevented from detecting errors, and also from logging and displaying diagnostic trouble codes (DTCs). To program the CECU and enable gauges, select “Program”. If the gauge value is “Disable”, change it to “Enable”.
Once the CECU is programmed and the link to the gauge is “enabled”, the CECU monitors it, diagnoses errors like “shorts” and “opens”, logs DTCs for troubleshooting, and displays the DTCs on ESA’s “Diagnose” screen.
5 - 2 PM819023/KM815057 (08/14/2012) Network Description What’s on the Network V-CAN Vehicle powertrain Transmission Engine ABS telematics (optional)¹ D-CAN Diagnostic Diagnostic connector F-CAN Frame components Chassis Node I-CAN Instruments Instrument cluster C-CAN Cab PACCAR Display or Radio Door controllers HVAC Remote Sleeper Audio (optional) Multifunction steering wheel (optional) B-CAN Body Builder Aftermarket devices² E-CAN Engine Input Turbo Humidity Sensor EGR A-CAN³ Aftertreatment NOx sensors Doser Control Unit Aftertreatment control unit ¹Not all telematics units will be recognized by the CECU architecture.
²Telematic units connected to the BCAN will not be recognized by the CECU. Any device spliced into a CAN wire will not be recognized by the CECU architecture. ³For vehicles built with PACCAR MX engine.