Note On Intermittent (Toronado):

If circuit No. 685 was intermittently grounded, Code B123 could be stored. Manipulate circuit No. 685 while observing BI01 with the dimmer at a low setting. If the short occurs, the value will switch from "HIGH" to "LOW".

Also check BCM data BD42. Cycle panel dimming control from minimum to maximum. If BD42 does not read 2-98%, then replace left switch assembly.