K 1500 Truck 4WD V8-6.5L DSL Turbo VIN S (1999)
Information Bus: Description and Operation
The Data Link Connector DLC connection is used as an access point for different vehicle diagnostic and programming functions, including those
involving the use of a scan tool. Three different types of Serial Data Communications are accessible through the DLC.
UART
The UART Serial Data communication relies on a 5 volt digital signal for the exchange of data between different control modules and to provide
scan tool diagnostic data. When the ignition switch is in the RUN position and the UART line is at rest, i.e. no communication taking place, the
voltage remains HIGH at approximately 5 volts. When data is transmitted the voltage is pulled to ground, approximately 0 volts.
The Supplemental Inflatable Restraint System's Sensing and Diagnostic Module (SDM) utilizes UART communications. The SDM uses UART
serial data to allow communication with a scan tool for diagnostic purposes. Diagnostic Trouble Codes (DTC's) stored by the SDM can be
retrieved, viewed and cleared with the use a scan tool. A loss of UART communications would prevent the scan tool from communicating with the
SDM during SIR system diagnosis.
Class 2
Modules on the Class 2 Data Line use State of Health communication messages to control and monitor other modules. Some control modules on
the Class 2 communication system have the ability to recognize other modules that are no longer communicating. When this problem occurs, the
module(s) that recognize the problem may store one or more DTC's identifying the failed module. From the beginning of a power mode,
communications between modules continues every 2 seconds. If the communication time between modules passes 5 seconds a State of Health
DTC will set.
Failure to communicate with the Class 2 data circuit could be anyone of the following faults:
^
A faulty Class 2 data line, CKT 1807 (PPL)
^
A fault in the modules power circuit
^
A fault in modules ground circuits
^
A faulty control module
Communication failure DTC's are identified as 5 digit codes, with the first digit being U. The remaining digits are numeric and refer to the specific
system that has failed.
E&C Bus
The Entertainment and Comfort (E&C) Bus has limited function capability. By connecting a scan tool, the radio receiver can be requested to
transmit it's hardware, software, and calibration values through the E&C Bus to the scan tool.
Remote Control Door Lock Receiver (remote Keyless Entry) Programming
The DLC provides a connection to the Remote Control door Lock Receiver to allow the programming of the receiver to recognize the specific
Remote Control Door Lock Transmitters used. If the Remote Control Door Lock Receiver will not respond to programming input, refer to Unable
to Reprogram Remote keyless Entry Control Module diagnostic table.
Selectable Transfer Case Control Module (TCCM) Diagnostics
The Selectable Transfer Case Control Module has limited self-diagnostic capabilities. If the TCCM diagnostics are not functioning properly follow
Obtaining Diagnostic Trouble Codes. Refer to Obtaining Diagnostic Trouble Codes. See: Testing and Inspection
