Scan Tool Does Not Communicate With Class 2 Device

Scan Tool Does Not Communicate W/Class 2 Data Line:

Scan Tool Does Not Communicate W/Class 2 Data Line:

Scan Tool Does Not Communicate W/Class 2 Data Line:

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 Lost Communications with 1XXX diagnostic table in order to diagnose the malfunction.

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 (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 module's 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 2 seconds. When no message is detected from a learned identification number for 5 seconds, a DTC U1XXX (where XXX is equal to the three digit identification number) is set.

Conditions for Running the DTC
^ Voltage supplied to the module is in the normal operating voltage range (approximately 9 - 16 volts).
^ The vehicle power mode (ignition switch position) requires serial data communication to occur.

Conditions for Setting the DTC
A message from a learned identification number has not been detected for the past 5 seconds.

Conditions for Clearing the DTC
^ A current DTC will clear when a Node Alive message from the failed identification number is detected on the class 2 serial data circuit or at the end of the current ignition cycle.
^ A history DTC will clear upon receipt of a scan tool Clear DTCs command.

Diagnostic Aids
^ An intermittent open, short to ground, or short to B+ between the inoperative module and the data line may cause this code to set.
^ A poor connection at the inoperative module or the data line may cause this code to set.
^ An intermittent open in the data line may cause this code to set.

Test Description
1. A module which loses power during an ignition cycle will cause other module(s) to set Lost Communication DTCs.
2. The malfunction may be due to an open in the class 2 serial data circuit or an open in the module circuit.
6. The module which was not communicating due to an open in the class 2 serial data circuit and may have set Lost Communication DTCs for those modules that it was monitoring.
8. The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.