Important: The following steps must be completed before using the symptoms tables.
- Perform the 
Diagnostic System Check - Vehicle
 before using the symptom tables in order to verify that all of the following are true:
 
| •  | The control modules can communicate via the serial data link. | 
 
- Review the system operation in order to familiarize yourself with the system functions. Refer to the following:
 
Visual/Physical Inspection
Several of the symptom procedures ask for a careful visual/physical check. This step is extremely important. It could lead to correcting a problem without further checks and can save valuable time. These checks include the following:
|     •  | Inspect the easily accessible or visible system components and harness connectors for obvious damage or conditions which could cause the symptom. | 
 
|     •  | If only one lamp is inoperative, inspect and repair a poor connection or an open in the power feed or ground circuit before replacing the light bulb. Refer to 
Circuit Testing
 and 
Wiring Repairs
 . | 
 
Intermittent
 Faulty electrical connections or wiring may also be the cause of intermittent conditions. Refer to 
Testing for Intermittent Conditions and Poor Connections
 .
Symptom List
Refer to a symptom diagnostic procedure from the following list in order to diagnose a symptom that does not set a DTC: