Class 2 Serial Data Line
Modules communicate along one common Purple wire referred to as class 2 serial data line. Serial data line is used to communicate information between systems. Each system on the serial data line is assigned its own identification number, which is used to identify itself to other modules or systems. Class 2 serial data line also allows communication with scan tool through Data Link Connector (DLC). See Figure . Modules communicating along class 2 serial data line are as follow:
- Cellular Telephone Module
- Continuously Variable Road Sensing Suspension (CVRSS) Module (With F45)
- Dash Integration Module (DIM)
- Driver Door Module (DDM)
- Electronic Brake Control Module (EBCM)
- Instrument Panel Integration Module (IPM)
- Instrument Cluster
- Memory Seat Module (MSM)
- Navigation Data Processor (With UY4)
- Navigation Display Module (With UY4)
- Navigation Radio (With UY4)
- Powertrain Control Module (PCM)
- Radio
- Radio Amplifier
- Rear Integration Module (RIM)
- Remote Keyless Entry (RKE)
- Sensing And Diagnostic Module (SDM)
- Steering Column Module
- Theft Deterrent Module
- Vehicle Interface Unit (With UE1)
When ignition is on, each module communicating on the class 2 serial data line sends a State Of Health (SOH) message every two seconds to ensure that the module is operating properly. When a module stops communicating, for example if module loses power or ground, SOH message normally sent on the data line every two seconds disappears. Other modules on the class 2 serial data line which expect to receive that SOH message, detect its absence and in turn set an internal DTC (Diagnostic Trouble Code) associated with loss of SOH of the non-communicating module. The DTC is unique to the module which is not communicating.
For example, when the Dash Integration Module (DIM) SOH message disappears, several modules will set DTC U1064 Loss Of Communication With DIM. Loss of serial data DTCs do not normally represent a failure of the module that set the DTC. Use this technique to quickly identify which module is not communicating on the class 2 serial data line.