Circuit Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring. These messages are also known as node alive messages. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, it will monitor for that modules node alive message.

Each module on the class 2 serial data circuit which is powered and performing functions that require detection of a communications malfunction is required to send a node alive message every two seconds. When no message is detected from a learned identification number for five seconds, a DTC U1xxx is set.

The control module ID number list provides a method for determining which module is not communicating. A module with an internal class 2 serial data circuit malfunction or which loses power during the current ignition cycle would have a lost communication DTC set by other modules. Use the control module ID number list in order to determine which module is not communicating and the DTC U1001-U1254 diagnostic table in order to diagnose the malfunction.

When more than one loss of communication DTC is set in a single module or among multiple modules, diagnose the DTCs in the following order:

• Current DTCs before history DTCs except as specified in the diagnostic tables.
• The DTC which is reported the most times.
• From the lowest number DTC to the highest number DTC