Important: For the inside rearview mirror with the automatic day-night feature  or the rear window defogger (w/o C68), review the system operation   in order to familiarize yourself with the system  functions. Refer to the   following:
For the rear window defogger (w/ C68) system, perform the following  steps before using the symptom tables.
- Perform 
Diagnostic System Check - Defogger 
 before using the symptom tables in order to verify that all of  the following conditions are true:
 
| •  | The control modules can communicate via the serial data link. | 
 
- Review the rear window defogger system operation in order to familiarize  yourself with the system functions. Refer to 
Rear Window Defogger Description and Operation 
.
 
Visual/Physical Inspection
|     •  | Inspect for aftermarket devices which could affect the operation  of the rear window defogger or the automatic day-night feature of the inside    rearview mirror. Refer   to 
Checking Aftermarket Accessories 
  in Wiring Systems. | 
 
|     •  | Inspect the easily accessible or visible system components for  obvious damage or conditions which could cause the symptom. | 
 
Intermittent
Bad electrical connections or bad 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: