Testing Diode Trio
WARNING: This page is about a different car, the 2002 Subaru Impreza, 2002 Subaru Forester, 2001 Subaru Impreza, and 2001 Subaru Forester. However, it is still accessible from the selected car via links, so may be relevant.
To check diode trio, remove diode assembly from rear cover. Using an ohmmeter, check each diode for continuity. Continuity should be present in one direction only. If continuity is present in both directions, or continuity does not exist in either direction, diode trio is faulty. If any diode is faulty, replace complete rectifier assembly.