P0625
Generator Field/F Terminal Circuit Low
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The P0625 code means the PCM has detected a lower-than-expected voltage on the alternator's field terminal (also called the F terminal) circuit. The field terminal controls the electromagnetic field inside the alternator — by varying the current to the field coil, the PCM can precisely control how much electrical power the alternator produces. A low reading means the field circuit is not receiving or producing enough voltage.
When the field circuit voltage is low, the alternator may not be charging the battery adequately. You'll likely notice the battery warning light on the dashboard, dimming headlights (particularly at idle), and the battery may drain overnight or over a few days. Electrical accessories like power windows and the radio may work intermittently or slowly. If the charging deficit is severe enough, the engine could stall when the battery is fully depleted.
Begin diagnosis by checking the serpentine belt condition and tension, then have the battery and alternator tested (many auto parts stores do this for free). Inspect the wiring and connector at the alternator's field terminal for corrosion, damage, or loose connections. Clean all engine and alternator ground straps. If the alternator's internal voltage regulator has failed, the entire alternator typically needs to be replaced, as the regulator is usually not serviceable separately on modern vehicles. This is a moderately DIY-friendly repair for someone comfortable with basic electrical testing and belt/alternator replacement.
Severity
Symptoms
- •Battery warning light illuminated on the dashboard
- •Check engine light illuminated
- •Dim headlights, especially at idle
- •Battery keeps dying or vehicle won't start after sitting
- •Electrical accessories lose power or work intermittently
- •Reduced fuel efficiency
Likely Causes
The field terminal (F terminal) controls the magnetic field strength inside the alternator. If the alternator's voltage regulator or rotor winding has failed, it cannot generate the proper field voltage, resulting in a low reading at the F terminal.
The wiring from the PCM to the alternator's field terminal can develop corrosion, breaks, or shorts over time, preventing the proper control voltage from reaching the alternator.
A serpentine belt that is worn, cracked, or improperly tensioned may slip on the alternator pulley, preventing the alternator from spinning at the required speed to generate adequate field voltage.
The alternator needs a solid ground to complete the field circuit. Corroded or loose engine-to-chassis ground straps will cause voltage drops that appear as low field terminal voltage.
The PCM's internal driver that controls the field terminal voltage may have failed, or the PCM's monitoring circuit may be incorrectly reading the voltage as low.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Test and replace the alternator if the internal regulator or rotor has failed
- Inspect and repair the wiring and connector at the alternator field terminal
- Replace or tension the serpentine/drive belt
- Clean and secure all alternator and engine ground connections
- Test the battery and replace if it can no longer hold a proper charge