A series of molecular signals initiated by binding of a ligand to a ERBB3 receptor on the surface of a cell, followed by transmission of the signal by a heterodimeric complex of ERBB2 and ERBB3. ERBB2, which does not bind any known ligand, is activated through formation of a heterodimer with another ligand-activated ERBB family member such as ERBB3. ERBB3 also has impaired kinase activity and relies on ERBB2 for activation and signal transmission.