OBD-II Code P0625 — What It Means & How to Fix It

What Does This Error Mean?

P0625 means the generator (alternator) field terminal circuit is reading a voltage that is too low. The field terminal is the control wire that tells the alternator how much electricity to produce. When voltage on this wire is lower than expected, the ECM logs P0625. This can mean the alternator is not charging properly, which will eventually drain the battery. Common causes include a faulty alternator, bad wiring, or a poor connection at the field terminal.

Affected Models

All vehicles 1996+
Common in GM vehicles with Delco-Remy alternators
Common in Ford vehicles
Common in Chrysler and Dodge vehicles
Common in vehicles with externally regulated charging systems

Common Causes

Faulty alternator with internal field circuit failure causing low control voltage
Short to ground on the field terminal control wire
Corroded or loose field terminal connector at the alternator
Damaged wiring harness between the ECM and the alternator field terminal
Failing ECM output for the alternator field control

How to Fix It

Locate the alternator and identify the field terminal — the smaller of the wires at the alternator connector. Check the connector for corrosion or loose fit.

The field terminal wire is typically a smaller gauge than the main charging output wire.
Unplug the alternator connector. With the key on and engine off, measure voltage at the field terminal pin in the harness connector. It should show near 12V or a 5V reference depending on the system.

No voltage at this pin with the connector unplugged points to a wiring or ECM problem, not the alternator.
Inspect the wiring from the alternator connector back toward the ECM. Look for chafed, pinched, or corroded wires along the harness.

The alternator wiring is exposed to engine heat and vibration — both cause deterioration over time.
Check charging system voltage with the engine running. If charging voltage is low (below 13.5V) or non-existent, the alternator field circuit has likely failed internally.

A complete loss of charging with P0625 strongly suggests alternator replacement is needed.
Replace the alternator if internal failure is confirmed. Use a direct OEM-equivalent unit. Clear the code and test drive to confirm charging voltage returns to normal.

Have the battery tested too — if it has been undercharged for a while, it may need replacement as well.

When to Call a Professional

Alternator and wiring repairs are within DIY capability for most people. Remanufactured alternators cost $100 to $300 for the part. Labor at a shop is $100 to $250. Wiring repairs typically cost $75 to $150 in labor. Always have the charging system tested after any alternator-related repair.

Frequently Asked Questions

What does the alternator field terminal do?

The field terminal carries a control signal that tells the alternator how hard to work. When the battery is low or electrical demand is high, the ECM sends a stronger signal through the field terminal. This causes the alternator to produce more electricity. Without a proper field signal, the alternator cannot regulate its output.

Will P0625 leave me stranded?

Possibly, over time. If the alternator stops charging, the battery will drain. Once the battery is dead, the car will not start. Monitor your battery warning light and get the charging system checked promptly.

Is P0625 the same as P0626?

They are closely related. P0625 is for a low voltage condition on the field terminal circuit. P0626 is for a high voltage condition on the same circuit. Both point to problems with the alternator's control wiring or the alternator itself.