P0625

What it means

P0625 means the engine control unit has detected a low voltage or signal level on the generator (alternator) field control circuit, often called the F terminal. The ECU uses this circuit to monitor or command the alternator's output, and it set the code when the signal stayed lower than expected for the conditions. How the circuit works varies between vehicles, so the exact fault depends on the model and alternator type.

Symptoms

• Battery or charging warning light on the dashboard
• Flat or weak battery, slow cranking
• Dim headlights or electrical items working poorly
• Engine management light on
• Erratic idle or stalling in some cases due to low system voltage
• Charging voltage too low or not controlled properly

Possible causes

• Wiring fault in the field/F terminal circuit, such as a short to earth, chafed insulation or open circuitlikely
• Corroded, loose or damaged connector at the alternator or ECUlikely
• Faulty alternator, including an internal regulator failurelikely
• Poor earth connection or high resistance in the charging circuitpossible
• Weak or failing battery causing abnormal charging demand and voltage readingspossible
• Faulty ECU or driver circuit inside itrare

How to diagnose

1. Read all stored codes and freeze frame data, noting battery voltage, engine speed and load when the code set, and check for other charging or voltage codes
2. Check the battery condition and state of charge, and measure resting voltage
3. Visually inspect the alternator connector, wiring and harness for chafing, heat damage, corrosion and water ingress
4. Measure battery voltage with the engine running at idle and with loads on to check that the alternator is charging; the expected figure depends on the model
5. Check the battery, engine and chassis earth connections for security and voltage drop
6. Using the manufacturer's wiring diagram, test the F terminal wire for continuity, short to earth and short to supply, with the connector disconnected
7. Check the ECU command against the alternator response using live data, if the vehicle supports it
8. Test the alternator output and regulator following the procedure for that model

How to fix

• Repair or replace damaged wiring and terminals in the field circuit
• Clean, secure or replace the corroded or loose alternator and ECU connectors
• Replace the alternator or its regulator if it fails testing
• Repair poor earth or power connections that cause voltage drop
• Replace the battery if it is weak or failing, then recheck the charging system
• Only after all else is ruled out, diagnose and repair or replace the ECU as directed by the manufacturer

Can I keep driving?

Nearby codes

• P0624GenericFuel Cap Lamp Control Circuit
• P0626GenericGenerator Field/F Terminal Circuit High