Astra L4-1.8L (2009)
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Do not replace a control module reporting a U code. The U code identifies which control module needs to be diagnosed for a communication
issue.
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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.
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An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle. When the scan tool
attempts to communicate with the vehicle a message "no CANdi module detected" will be displayed.
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The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus.
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Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) and no low speed GMLAN
communications with the scan tool.
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The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus.
These conditions may be caused by the installation of an aftermarket navigation radio module (see bulletins). Some customers may comment of
one or more of the following concerns:
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Vehicle will not crank.
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Vehicle cranks but will not start.
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Vehicle stability enhancement system warning lights and messages.
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PRNDL gear indicator position errors.
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Tire Pressure Monitor (TPM) system warning lights.
Reference Information
Schematic Reference
Data Communication Schematics (See: Diagrams/Electrical Diagrams)
Connector End View Reference
Component Connector End Views (See: Diagrams/Connector Views)
Description and Operation
Data Link Communications Description and Operation (See: Description and Operation)
Electrical Information Reference
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Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics)
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Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics)
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Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics)
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Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information
Circuit/System Verification
Attempt to communicate with all modules on the mid speed GMLAN bus.
If any high speed module communicates and any DTC beginning with a U exists, refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: Testing
and Inspection/Diagnostic Trouble Code Descriptions).
Circuit/System Testing
1. Ignition OFF, test for less than 1.0 ohm between the data link connector (DLC) ground circuit terminal 5 and ground.
‹› If greater than the specified range, test the ground circuit for an open/high resistance.
2. Ignition OFF, disconnect the X1 harness connector at the infotainment display.
3. Ignition OFF, test for less than 2 ohms between the DLC serial data circuit terminals and the CIM serial data circuit terminals listed below:
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DLC terminal 3 and CIM terminal 22
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DLC terminal 11 and CIM terminal 23
‹› If greater than the specified range, test the serial data circuit for open/high resistance.
4. Ignition OFF, test for infinite resistance between the following serial data circuits of the DLC and ground.
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Terminal 3
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Terminal 11