P0625Generic code

P0625 Code: Generator Field/F Terminal Low

The P0625 code means the computer sees low voltage in the alternator control circuit, caused by a short to ground or a lack of power. It can make the battery stop charging or overcharge. Check the fuse, relay, connector and wiring first.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$30 to $700
Difficulty
Medium
System
Computer and Outputs
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0625 code means

On many modern vehicles the computer controls how much the alternator charges. It sends a command signal (a field terminal or a LIN communication line) and gets a status signal back. That lets it adjust the charging voltage to the temperature, the electrical load and the condition of the battery.

The computer watches the control circuit from its own driver transistor. The P0625 code flags low voltage in that control circuit, either a short to ground or a lack of power. Before you replace the component, check the fuse, relay, connector and wiring, which are the most common causes.

If communication with the alternator fails, it usually charges at a fixed safe voltage, or it stops charging and the battery light comes on. Always measure the charging voltage with the engine running. It is the quickest way to find out whether the alternator is charging.

To confirm the fault, unplug the component with the key on and see what happens to the reading or the code. If the value jumps to the opposite extreme, the wiring is good and the component is the one pulling the signal to ground. If nothing changes, look for the short in the wire, starting where the harness rubs against the engine, the chassis or the exhaust.

P0625 code symptoms

  • Check engine light or another warning light on.
  • The battery does not charge, or it overcharges.
  • Battery light on.
  • A battery that keeps going flat.
  • A fixed or abnormal charging voltage.

Likely causes of the P0625 code

  1. Control wire shorted to ground. The component may stay on all the time, or the computer cuts the command to protect itself.
  2. Interrupted power supply. A blown fuse, a faulty relay or a cut wire.
  3. Shorted component. Its resistance is much lower than specified.
  4. Connector with moisture. It creates a path to ground.

How to diagnose the P0625 code step by step

  1. Activate the component with the scan tool and check whether it responds.
  2. Check the fuse and relay. Measure the voltage on both sides of the fuse, and swap the relay with an identical one.
  3. Measure the supply at the connector. You should see battery voltage with the key on or when the component is activated.
  4. Measure the resistance of the component and compare it with the manual. Also check the insulation to ground.
  5. Check the control wire for continuity to the computer and for shorts.
  6. Measure the charging voltage with the engine running: 13.5 to 14.7 volts.
  7. Inspect the small connector on the alternator. It tends to corrode.

How to fix the P0625 code

  • Repair the connector, the wiring or the power supply.
  • Replace the alternator (computer controlled) if it does not respond even with correct power and command signals.
  • Clear the codes and verify the repair.

Technical reference data

  • Normal charging voltage: 13.5 to 14.7 volts (it varies on managed charging systems).
  • Reference values: check the manufacturer data for your vehicle.

Brand-specific notes

This code is common on several makes. The control method differs, so make sure you know which kind of alternator control your vehicle uses before you start testing.

P0625 on Ford

Very common on Ford, where the computer commands the alternator through a control terminal.

P0625 on GM

Also common on GM vehicles, which use the same kind of computer controlled charging.

P0625 on Volkswagen

Common on Volkswagen, where the alternator is commanded over a LIN line.

Frequently asked questions about P0625

Can I drive with a P0625 code?
With caution. If the alternator is not charging, the vehicle will run only until the battery goes flat, so keep trips short and head to a shop.
What does the alternator control circuit do?
On many modern vehicles the computer controls the alternator. It sends a command signal and receives a status signal back, so it can adjust charging to the temperature, the load and the battery condition.
Do I always have to replace the alternator?
No. Check the fuses, relays, connectors and wiring first, because they are the most common cause.
How much does it cost to fix P0625?
As a rough guide, between $30 and $700. A fuse or connector repair is at the low end, and a new alternator is at the high end.
What does the P0625 code mean?
It is a generic OBD2 code that means the computer sees low voltage in the alternator control circuit, from a short to ground or a loss of power.
What is the most common cause of P0625?
With a P0625 code, the usual culprit is a control wire shorted to ground, a blown fuse or a faulty relay. Moisture in a connector can also create a path to ground.

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