- Perform the 
Diagnostic System Check - Lighting Systems 
 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
|     •  | Inspect the easily accessible or visible system components for    obvious
damage or conditions which could cause the symptom. | 
 
Intermittent
Faulty electrical connections or wiring may be the cause of intermittent   
conditions. Refer to 
Testing for Intermittent Conditions and Poor Connections 
 in Wiring Systems.
Symptom List
Refer to a symptom diagnostic procedure from the following list in order   
to diagnose the symptom: