Circuit Description
Modules connected to the Class 2 data link monitor the link for serial
data communications during normal vehicle operation. Operating information
(Report messages) and commands (Load messages) are exchanged among the modules.
When the inflatable restraint Sensing and Diagnostic Module (SDM) receives
a Report or Load message for a critical operating parameter, the SDM records
the Source ID of the module which sent the message for State Of Health (SOH)
monitoring (Node Alive messages). The SDM Does this after each ignition cycle.
A critical operating parameter is one which, when not received, requires that
the module use a default value for that parameter. Once a Source ID is learned
by a module, it will monitor for that Source ID's SOH message. Each module
on the Class 2 data link which is powered and performing functions that require
detection of communication malfunctions is required to send a SOH message
every two seconds. When no message is detected from a learned Source ID, in
this case the Body Control Module (SBM), for five seconds, a DTC U1064 is
set. For more detailed information about the data lines, refer to Data Link
Connector -- Cell 50.
Conditions for Setting the DTC
| • | Voltage supplied to the SDM is in the normal operating voltage
range (approximately 9-16 volts). |
| • | DTC U1300 and DTC U1301 are not current. |
| • | The SDM does not detect a learned Source ID message from the SBM
for 5 second. |
Action Taken When the DTC Sets
The SDM sets DTC U1064.
Conditions for Clearing the MIL/DTC
The DTC will clear when one of the following conditions is met:
| | The SDM receives a SOH message from the SBM or the ignition
switch is turned to the OFF position. |
| | You issue a scan tool CLEAR CODES command. |
Diagnostic Aids
The following failures could cause a history DTC U1064 to set.
| • | The SBM lost B+ or ground with the ignition switch in the RUN
position. |
| • | A poor connection at the SBM caused both Class 2 Serial Data
Lines to open with the ignition in the RUN position. |
Check that the SBM is functioning properly. Use the SOH DTC diagnostic
information in Data Link Connector - Cell 50 and the the SBM Diagnostic System
Check in Body Control Module -- Cell 51.
