For 1990-2009 cars

### Diagnostic Instructions

• | 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 12V 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 connections/connectors for the area of concern are fully seated. Refer to Component Connector End Views.

• | 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.

### Diagnostic System Check

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.

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. 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 Power Mode Mismatch.

5. 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.

6. CONTROL MODULE COMMUNICATION VERIFICATION--Verify the vehicle is built with any control module listed as not communicating, refer to Data Link References. All control modules should be communicating, as equipped.

⇒ | If the scan tool does not communicate with one or more control modules refer to Data Link References.

7. 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.

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.

8. POWER MODE VERIFICATION--Driver door open, observe the scan tool Power Mode parameter while cycling the ignition switch through all the power modes. Verify the current Power Mode parameter matches the actual ignition switch positions.

⇒ | If the Power Mode parameter does not match the actual ignition switch positions, refer to Power Mode Mismatch.

9. 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.

10. 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.

10.1. | Voltage DTCs

10.2. | Programming, Setup, Configuration or Software Performance DTCs

10.3. | Component related DTCs

10.4. | System related DTCs

10.5. | Any remaining DTCs

11. 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 (I/M) System Check.

12. SYMPTOM DIAGNOSIS--Diagnose any remaining customer concern. Refer to Symptoms - Vehicle.