Important Preliminary Inspections Before Starting

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Before using the Symptom diagnosis, perform the following:

Perform Diagnostic System Check - Vehicle (with HP2) , Diagnostic System Check - Vehicle (without HP2) and verify all of the following items:
- Ensure that the engine control module (ECM) and indicator lamp are operating correctly.
- Ensure that there are no diagnostic trouble codes (DTCs) that are stored.
- Scan tool data is within a normal operating range. Refer to Control Module References for scan tool information.
Verify the customer concern.
Perform the Visual/Physical Inspection in this section. The visual/physical inspection is extremely important, and can lead to correcting a condition without additional testing. It may also help reveal the cause of an intermittent condition.
Locate the correct symptom. Perform the tests and inspections associated with the symptom.

Review the system operation in order to familiarize yourself with the system functions. Refer to Cooling Fan Description and Operation (Gas) .