Note on Intermittents
WARNING: This page is about a different car, the 1990 Buick Riviera and 1990 Buick Reatta. However, it is still accessible from the selected car via links, so may be relevant.
If circuit No. 685 were intermittently grounded, Code B123 could be stored. Manipulate circuit No. 685 while observing BI01 display with dimmer at a low setting. If short occurs, value will switch from HI to LO.
Also check BD42 display. Cycle panel dimming control from minimum to maximum. If BD42 display does not range between 2-98 percent, or never reads more than 75 percent, replace left switch assembly.