P0625

P0625 indicates the generator field terminal (the F terminal that PCM-controlled alternators use to command field current via PWM) is reading lower than expected, suggesting either a shorted-to-ground field driver, a failed regulator inside the alternator, or an open in the control wire from the PCM to the alternator. Cheapest-first: with the engine running, measure charging voltage at the battery — it should be 13.5-14.7V on a healthy system. If it is at or below battery voltage (12.0-12.4V), the alternator is not field-energized. Back-probe the F-terminal wire at the alternator and look for a PWM signal that varies with electrical load (turn on headlights and rear defroster — duty cycle should increase). No signal at the alternator means the PCM driver or wiring is at fault; signal present but no charging means the alternator's internal regulator is failed. Inspect the alternator connector for corrosion and burnt pins — a heavily loaded charging system at high temperatures cooks these connectors regularly. Verify battery voltage is 12.4V+ at rest before condemning the alternator, because a deeply discharged battery can pull the field driver into a fault condition that mimics P0625. The expensive misdiagnosis is replacing the alternator without checking the connector and wiring — install a new alternator into a corroded connector and the same code returns within days.

Vehicle-specific patterns: 2006-2013 GM trucks and SUVs (Silverado, Tahoe, Suburban) with PCM-controlled alternators commonly set P0625 from internal regulator failure in the AD244/AD230 alternator, documented in GM bulletin 09-06-03-005. 2005-2010 Ford F-150 and Expedition with the 6G alternator throw P0625 from corroded 4-pin alternator connectors at the regulator, addressed by Ford TSB 10-22-1 with a pigtail repair kit. 2007-2014 Chrysler/Dodge/Jeep with the dual-purpose regulator throw P0625 when the field circuit driver inside the PCM fails or when the alternator's internal voltage regulator shorts. 2005-2012 VW/Audi with the load-response regulator set P0625 from broken field wires at the alternator's terminal block. Estimated repair: $80 to $900.