H3 V8-5.3L (2008)
Circuit/System Description
Modules connected to the GMLAN serial data circuit monitor for serial data communications on the GMLAN network during normal vehicle operation.
Operating information and commands are exchanged among the modules. The high speed GMLAN serial data buss uses two 120 ohm terminating
resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is connected near the data link connector (DLC) end of
the link and the other is internal to the ECM/PCM, end of the link. When a module detects a bus-off condition a DTC U2100 will be set. This DTC can
be retrieved as history only.
Diagnostic Aids
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When testing for a short between the high speed GMLAN (+) and (-) circuits (ECM/PCM disconnected), a resistance reading of 120 ohms is
normal. To test for shorts to voltage or ground in the high speed GMLAN (+) and (-) circuits ensure that all modules, resistors and the scan tool
are disconnected from the buss. A normal resistance reading across the high speed GMLAN buss with the resistors, all module and scan tool
disconnected is infinite ohms.
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The engine may 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:
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A short between high speed GMLAN (+) and high speed GMLAN (-) circuits
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Any of the high speed GMLAN serial data circuits shorted to ground or voltage
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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)
Connector End View Reference
Component Connector End Views (See: Diagrams/Connector Views/Component Connector End Views)
Description and Operation Reference
Data Link Communications Description and Operation (See: Description and Operation)
Electrical Information Reference
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Circuit Testing (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Circuit Testing/Circuit Testing)
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Connector Repairs (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Connector Repairs/Connector Repairs)
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Testing for Intermittent Conditions and Poor Connections (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Circuit
Testing/Testing For Intermittent and Poor Connections)
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Wiring Repairs (See: Diagrams/Diagnostic Aids/General Electrical Diagnostic Procedures/Wiring Repairs/Wiring Repairs)
Scan Tool Reference
Control Module References (See: Testing and Inspection/Programming and Relearning)for Scan Tool Information
Circuit/System Testing
1. Test for less than 1.0 ohm of resistance between the DLC ground circuit terminal 5 and ground.
‹› If greater than the specified range, test the ground circuit for open/high resistance.
2. Ignition OFF, disconnect the harness connector X 3 at the engine control module (ECM).
3. Test for less than 1 ohm of resistance between each ground circuit of the ECM and ground.
‹› If greater than the specified range, repair the ground circuit for an open/high resistance.
4. Ignition ON, test for battery voltage between each voltage input circuit of the ECM and ground.
