Generator Field/F Terminal Circuit Low Voltage
The P0625 code indicates that the powertrain control module (PCM) has detected a low voltage condition in the generator field or F terminal circuit. This circuit controls the alternator's field current, which is necessary for charging the battery. A low voltage reading suggests a problem with the alternator, wiring, or PCM, potentially leading to battery drain and charging system failure.
1. Most Common Causes
- Short to ground in the alternator field (F) terminal circuit wiring
- Open circuit or high resistance in the wire between the PCM and the field terminal
- Corroded, damaged, or retracted pins in the alternator or harness connector
- Faulty alternator (internal field coil failure, worn brushes, or bad diodes)
- Defective voltage regulator (internal to the alternator or external type, depending on application)
- PCM internal failure in the generator field monitoring or control circuit
2. Symptoms You Will Notice
- Battery warning light illuminated on dashboard
- Battery not charging or dead battery
- Dimming headlights or electrical issues
- Engine stalling or difficulty starting
3. Step-by-Step Diagnosis
Step 1: Use a multimeter to check battery voltage (should be 12.6V key off, 13.5-14.5V engine running).
Step 2: Inspect the alternator field circuit wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the alternator output and field circuit with a scan tool or multimeter; check for voltage at the F terminal.
Step 4: If wiring is intact, test the alternator's internal regulator and field winding; replace alternator if faulty.
Step 5: Check fuses and fusible links related to the charging system; replace if blown.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
No, it is not safe. The vehicle may stall or leave you stranded due to a dead battery. Have it diagnosed and repaired promptly.
How much does it cost to fix?▼
Typically $50-$150 for diagnosis and minor repairs like wiring or fuses; alternator replacement can cost $200-$500.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.