What it means
Voltage on the alternator F terminal (field excitation) is below threshold — open or short to ground in the excitation path.
At a glance
- Usually lights the check-engine light
How it works
The alternator F terminal carries the field-excitation signal that helps regulate charging output. P0625 is set when the ECM detects the F-terminal circuit voltage is too low, which can result from an open or grounded circuit, poor contact, or a field component that cannot respond.
Common causes
Most likely first.
- Field circuit open or shorted to ground
- Alternator brushes worn
- Connector pins corroded - high contact resistance
Symptoms
- Charging-system warning light may illuminate
- Battery may discharge if the generator field is not controlled correctly
How to diagnose it
- Record freeze-frame data and check charging voltage and related generator codes to see whether the low field signal coincided with weak charging.
- Inspect the F-terminal connector and harness for corrosion, pushed-back pins, chafing, or a wire shorted to ground.
- Check alternator and battery grounds for high resistance or loose connections.
- Compare F-terminal voltage or field data with charging output in live data under the conditions in the freeze frame, where available.
- Test the F circuit for an open or short to ground and check the alternator brushes and regulator against the manufacturer's specification.
Common fixes
- Clean corroded F-terminal pins and secure the connector.
- Repair an open or short-to-ground in the field wiring.
- Restore a poor ground or high-resistance connection.
- Replace the alternator or regulator if worn brushes or an internal field fault are confirmed.
Can I keep driving?
If the charging warning light is on or the battery voltage is falling, limit driving and electrical use because the vehicle may stall after the battery discharges. Get the charging fault checked promptly.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.