Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Lack of communication may be due to a partial malfunction or a total malfunction of the class 2 serial data circuit. The specified procedure will determine the condition.
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This step will determine which version of OnStar® is installed on the vehicle and which set of diagnostic procedures should be used.
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The presence of DTCs which begin with "U" indicate some other system control module is not communicating.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: OnStar Schematics | |||
1 | Install a scan tool. Does the scan tool power up? | Go to Step 2 | Go to Scan Tool Does Not Power Up in Data Link Communications |
Does the scan tool communicate with the OnStar® module? | Go to Step 3 | Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications | |
3 |
Important: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode.
Does the ignition switch parameter reading match the ignition switch position for all switch positions? | Go to Step 4 | Go to Power Mode Mismatch in Body Control System |
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Important: This vehicle will be equipped with one of two OnStar® systems, Generation 4 or Generation 5. Access the Module 2, Module I.D. Information screen on the scan tool to determine which system the vehicle is using. The coordinating diagnostic procedures should be used. Select the display DTCs function on the scan tool. Does the scan tool display any DTCs? | Go to Step 5 | Go to OnStar Symptom Diagnosis | |
Does the scan tool display any DTCs which begin with a "U"? | Go to Step 6 | Go to Step 7 | |
6 | Does the scan tool display DTC U1500? | ||
7 | Does the scan tool display DTC B1000, B1004, B1007, or B1009? | Go to Diagnostic Trouble Code (DTC) List in Body Control System | Go to Step 8 |
8 | Does the scan tool display DTC B1327 or B1328? | Go to Diagnostic Trouble Code (DTC) List in Engine Electrical | |
