GM Service Manual Online
For 1990-2009 cars only

Begin the system diagnosis with the Diagnostic System Check - Retained Accessory Power . The Diagnostic System Check will provide the following information:

    â€¢ Class 2 communication status
    â€¢ "U" codes which indicate module communication or circuit failure
    â€¢ "B" codes which indicate a possible body function or circuit failure
    â€¢ The status of any "U" or "B" codes