H2 V8-6.2L (2008)
Circuit/System Description
Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating
information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The high speed GMLAN serial
data circuits must be operational for the vehicle to start due to body control module (BCM) and engine control module (ECM) communications. The
vehicle theft deterrent (VTD) module and ECM exchange information using the BCM as the gateway module allowing communication between the high
and low speed serial data busses. The low speed GMLAN serial data circuit must also be operational for vehicle starting. The high speed GMLAN serial
data bus uses two 120 ohm terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits.
Diagnostic Aids
*
Communication may be available between the BCM and the scan tool with the high speed GMLAN serial data system inoperative. This condition
is due to the BCM using both the high and low speed GMLAN systems.
*
Use the Data Link References (See: Initial Inspection and Diagnostic Overview/Data Link References) to identify the high speed GMLAN serial
data modules.
*
This test is used for a total high speed GMLAN communication failure. If only one module is not communicating and sets no DTC, ensure that the
vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics.
*
An open in the DLC ground circuit terminal 5 will allow the scan tool to operate to set up the vehicle on the tool and then not communicate with
the vehicle. When the scan tool is to the point of communicating with the vehicle, a message on the scan tool will indicate "no CANdi module
detected" and will not communicate.
*
The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus.
The following conditions may cause a total loss of high speed GMLAN data communication:
-
A short between high speed GMLAN (+) and high speed GMLAN (-) circuits
-
Any of the high speed GMLAN serial data circuits shorted to ground or voltage
-
A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits
Reference Information
Schematic Reference
*
Data Communication Schematics (See: Diagrams/Electrical Diagrams)
*
Programming and Relearning (See: Testing and Inspection/Programming and Relearning)
Connector End View Reference
Component Connector End Views (See: Diagrams/Connector Views/Component Connector End Views)
Description and Operation
Data Link Communications Description and Operation (See: Description and Operation)
Electrical Information Reference
*
Circuit Testing (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Circuit Testing/Circuit Testing)
*
Connector Repairs (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Connector Repairs/Connector Repairs)
*
Testing for Intermittent Conditions and Poor Connections (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Circuit
Testing/Testing For Intermittent and Poor Connections)
*
Wiring Repairs (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Wiring Repairs/Wiring Repairs)
Circuit/System Testing
1. Test for less than 1.0 ohm between the DLC ground circuit terminal 5 and ground.
‹› If greater than the specified range, test the ground circuit for open/high resistance.
