Class 2 Serial Data Line

On vehicles that have several control modules connected by serial data circuits, one module is Power Mode Master (PMM). On Seville, PMM is Dash Integration Module (DIM). DIM receives 4 signals from ignition switch. To determine correct power mode, DIM uses these following circuits: accessory, crank, Ignition 1 and OFF/RUN/START voltages. Modules that depend exclusively on serial data messages for power modes stay in a state dictated by last valid DIM message until they can check for engine run flag status on serial data circuits. If DIM fails, modules monitor serial data circuit for engine run flag serial data. If an engine run flag serial data is true, indicating that engine is running, modules fail-safe to RUN. In this state modules and their subsystems can support all operator requirements. If engine run flag serial data is false, indicating that engine is not running, modules fail-safe to OFF-AWAKE. In this state modules are constantly checking for a change status message on serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle. Modules communicating along class 2 serial data line are as follows:

• Cellular Telephone Module
• Continuously Variable Road Sensing Suspension (CVRSS) Module
• Dash Integration Module (DIM)
• Driver's Door Module (DDM)
• Electronic Brake Control Module (EBCM)
• Instrument Panel Module (IPM)
• Instrument Panel Cluster (IPC)
• Memory Seat Module (MSM)
• Navigation Data Processor
• Navigation Display Module
• Powertrain Control Module (PCM)
• Radio
• Rear Integration Module (RIM)
• Remote Keyless Entry (RKE)
• Sensing & Diagnostic Module (SDM)
• Steering Column Module
• Theft Deterrent Module
• Vehicle Interface Unit (VIU)

When ignition is turned to RUN position, each module communicating on class 2 serial data line sends a State Of Health (SOH) message every 2 seconds to ensure that a module is operating properly. When a module stops communicating, for example if module loses power or ground, SOH message normally sent on data line every 2 seconds disappears. Other modules on class 2 serial data line which expect to receive that SOH message, detect its absence and in turn set an internal DTC associated with loss of SOH of a non-communicating module. A DTC is unique to a module which is not communicating.

For example, when DIM SOH message disappears, several modules will store DTC U1064 Loss Of Communication With DIM. Loss of serial data DTCs do not normally represent a failure of module that store DTC. Use this technique to quickly identify which module is not communicating on class 2 serial data line.