Alternator
Definition
The alternator is a belt-driven three-phase generator with a rectifier and voltage regulator that supplies the vehicle's electrical loads and recharges the battery, normally holding 13.8-14.8 V at the battery with the engine running. Modern units are controlled by the ECU or a LIN/BSS line to vary output for fuel economy and battery state, so a charging voltage of 12.8 V may be deliberate rather than a fault; check with a scan tool for the requested set point. Failures include worn brushes and slip rings, a failed regulator (over- or under-charging), open or shorted diodes (AC ripple over about 0.5 V, dimming lights, whining noise, battery drain), a noisy bearing and a seized overrunning alternator pulley (OAP) that causes belt chirp and vibration. Symptoms are a battery warning lamp, dim or flickering lights, repeated flat batteries and electronics acting up; always test ripple and voltage drop on the main cable and ground before replacing. Codes: P0620-P0626 (generator control circuit), P0562/P0563 (system voltage low/high), P2500-P2504 (generator lamp/field terminal), manufacturer codes for LIN communication with the regulator.