• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic System Check Instructions provides an overview of each diagnostic step.
• Continue through the Diagnostic System Check until you are directed to follow a particular diagnostic or repair procedure. Once a repair has been completed, perform the Diagnostic Repair Verification and verify the customer concern has been corrected.

The diagnostic procedures within this manual are developed on the assumption that the following areas function as designed:

• The 12 V battery is fully charged and cables are clean and tight. Refer to Battery Inspection/Test.
• Fuses are not open. Refer to Power Distribution Schematics and Electrical Center Identification Views.
• Ground circuits for the area of customer concern are clean, tight, and in the correct location. Refer to Ground Distribution Schematics and Harness Routing Views.
• All connectors/terminals fully seated in the area of concern. Refer to Master Electrical Component List.
• There are no aftermarket devices that affect the operation of the system. Refer to Checking Aftermarket Accessories.
• The scan tool powers up. Refer to Scan Tool Does Not Power Up.

1. VERIFY CUSTOMER CONCERN — Understand and validate the customer concern. Inspect the visible system components for obvious damage or conditions that may cause the concern.
2. BULLETIN SEARCH — Check for related bulletins, recall/field actions and preliminary information.
3. MECHANICAL CONCERNS — Verify the symptom is not exclusively a mechanical concern.
• If the symptom is exclusively a mechanical concern

  Refer to Symptoms - Vehicle.

• If the symptom is not a mechanical concern

Note: Do not clear any DTCs unless instructed to do so by a diagnostic procedure. If any DTC is Powertrain related, select Capture Info to store DTC and Freeze Frame/Failure Records to the scan tool.

4. VEHICLE POWER UP VERIFICATION — Vehicle in Service Mode, verify the vehicle powers up.
• If the vehicle does not power up

  Refer to Power Mode Mismatch.

• If the vehicle powers up
5. CONTROL MODULE COMMUNICATION and DTC CHECK — Using a scan tool, perform the Vehicle DTC Information function and verify at least one control module communicates with the scan tool. Record on the Repair Order the following information:
• Any control module that is not communicating.
• Any DTC, including symptom byte, and the control module that has set the DTC.
• If the scan tool does not communicate with any control module on the vehicle

  Refer to Data Link References.

• If the scan tool communicates with any control module
6. CONTROL MODULE INTERNAL PERFORMANCE FAULTS — Verify there are no current control module Internal Hardware Performance DTCs set.
• If any DTC of this type is set

  Refer to Diagnostic Trouble Code (DTC) List - Vehicle.

• If no DTC of this type is set
7. CONTROL MODULE COMMUNICATION VERIFICATION — Verify the vehicle is equipped with any control module identified as not communicating on the scan tool. For a list of all control modules the vehicle may be equipped with, refer to: Data Link References. With all non-communicating control module(s) identified, select the appropriate Data Communication schematic to determine the RPO(s) associated with the control module and verify the RPO is or is not present on the vehicle being diagnosed. All control modules should be communicating, as equipped.
• If the vehicle is equipped with a control module that is not communicating

  Refer to: Data Link References. Select the appropriate Scan Tool Does Not Communicate with Device on CAN link in the Diagnostic Procedure column.

• If all control modules the vehicle is built with are communicating
8. COMMUNICATION and POWERMODE FAULTS — Verify there are no current control module Power Mode or Communication DTCs set.
• If any DTC of this type is set

  Refer to Diagnostic Trouble Code (DTC) List - Vehicle.

• If no DTC of this type is set

Note: The engine may start during this test. Ensure the vehicle is out of gear and the parking brake is applied. Turn the engine OFF as soon as the crank power mode parameter has been observed.

9. POWER MODE VERIFICATION — Driver door open, observe each scan tool Power Mode data parameter while cycling through all power modes. Verify all Power Mode data parameters match the actual ignition switch/push button switch selection.
• If any Power Mode data parameter does not match

  Refer to Power Mode Mismatch.

• If all Power Mode data parameters match
10. PROACTIVE ALERT IDENTIFIERS—The technician is asked in this step to verify there are no Proactive Alert Identifiers set.  These identifiers are displayed on the scan tool and will only appear when the OnStar subscription is active and the customer has opted into the Proactive Alert service.
• If any Proactive Alert Identifier is set

  Refer to:Proactive Alerts List

• If no Proactive Alert Identifier is set
11. ENGINE CRANK and RUN VERIFICATION — Verify that the engine cranks and runs.
• If the engine does not crank

  Refer to Engine Does Not Crank.

• If the engine does not run

  Refer to Engine Cranks But Does Not Run.

• If the engine cranks and runs
12. REMAINING DTC REVIEW — Verify there are no other DTCs set.
• If other DTCs are set

  Diagnose them in the order listed below. Refer to Diagnostic Trouble Code (DTC) List - Vehicle.

1. Voltage DTCs
2. Programming, Setup or Configuration or Software Performance DTCs
3. Component related DTCs
4. System related DTCs
5. Any remaining DTCs
• If no other DTCs are set
13. EMISSION RELATED INSPECTION/MAINTENANCE TESTING CONCERNS — If inspection and maintenance checks are required in your region, verify the customer concern is not related to inspection/maintenance testing.
• If the customer concern is related to inspection/maintenance testing

  Refer to Inspection/Maintenance System Check.

• If the customer concern is not related to inspection/maintenance testing
14. SYMPTOM DIAGNOSIS — Diagnose any remaining customer concern. Refer to Symptoms - Vehicle.