Express 1/2 Ton Van V8-5.7L VIN R (1999)
Scan Tool Does Not Communicate With VCM/PCM (Vehicle Control Module)
Scan Tool Does Not Communicate With VCM/PCM (Vehicle Control Module)
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.
