VW T4 AAB Charging Issues Due to Worn Alternator Voltage Regulator

Confirm this cause by measuring the output voltage at the alternator B+ terminal while the engine is running. If voltage fluctuates significantly or fails to reach 13.5V despite a healthy belt and battery, the internal regulator brushes are likely worn. Inspect the regulator unit on the rear of the alternator for physical wear, carbon dust buildup, or uneven brush contact depth, which prevents consistent voltage regulation.