DTC B1278: Combination switch ECU communication stop: Wiring Diagram

WARNING: This page is about a different car, the 2003 Lexus LS 430. However, it is still accessible from the selected car via links, so may be relevant.

See DTC B1291 LIGHT SYSTEM COMMUNICATION BUS MALFUNCTION (+B SHORT), DTC B1292 LIGHT SYSTEM COMMUNICATION BUS MALFUNCTION (GND SHORT)