DTC B1251/51: Power Mirror Switch Circuit Malfunction: DTC Detecting Condition
WARNING: This page is about a different car, the 2002 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.
DTC B1251/51 is set on models with driver position memory system when communication between power mirror switch and body control ECU has stopped for more than 10 seconds.