2 Multiplexed Electrical System Service Manual Multiplexing Overview Models–Build Dates This manual provides service information covering trucks equipped with the multiplexed instrumentation system. Before attempting to make service repairs, the technician should be knowledgeable about the system design, components, operation and troubleshooting procedures for diagnosing multiplexed instrumentation problems. Identifying which control unit is in the vehicle helps determine what features are present and also aids in troubleshooting. How communication works in a multiplex system:
Each major subsystem in the truck’s electrical system is operated by a control module that sends and receives data to and from a central hub computer. The central hub computer is called the CECU (Cab Electronic Control Unit). Since we’re into the third generation now, we sometimes call it CECU3. The CECU receives data related to controlling the various devices of the electrical system. It then makes decisions based on that input and sends information to each of the subsystem system control modules (nodes) about what that node should do with the components it controls.
This new generation incorporates much of the same architecture from previous designs with added data communications with more control modules. The software has been upgraded to incorporate interlocks to ensure safety, maximize vehicle performance and simplify driver interaction. 2 - 2 PM819023/KM815057 (08/14/2012) Control Unit Hardware Part Number Software Version Models Engine Emissions Level Production Built Dates ICU Q21-1029-X-XXX P30-1003-XXX PB: 357, 378, 379, 385, 386 KW: C500, T600, T800, W900, Off-Highway 1998, 2004 2005 - 2006 CECU / CECU2 Q21-1055-X-XXX / Q21-1075-X-XXX P30-1002-XXX PB: 365, 367, 384, 386, 388, 389 KW:
C500, T440/T470, T660, T800, W900, Off-Highway 2007 2007 - 2009 PB: 387 KW: T2000 2008 - 2009 PB: 325, 330, 335, 340 2009 CECU3 Q21-1076-X-XXX P30-1008-XXX PB: 325, 330, 337, 348, 387 KW: T170, T270, T370, T700 2010 2010 - present CECU3 with Chassis Node Q21-1076-X-XXX with Q21-1077-X-XXX P30-1009-XXX PB: 365, 367, 384, 386, 388, 389 KW: C500, T440/T470, T660, T800, W900, Off-Highway 2010 2010 - present PB: 365, 367, 384, 386 KW: T660, T800 2010 2010 - 2011 CECU3 with Chassis Node Q21-1076-X-XXX with Q21-1077-X-XXX P30-1011-XXX PB: 579 KW: T680 2010 2011 - present