Generator Field/F Terminal Circuit Low
P0625 indicates the PCM detected low voltage or an open/shorted circuit in the alternator's field control circuit. This prevents proper charging system operation and can lead to battery discharge and electrical system failure if not addressed.
What You Might Notice
- Charging system warning lamp illuminated
- Battery not charging or undercharging
- Dimming headlights and interior lights
- Engine cranking slowly or difficulty starting
- Unexpected engine stalling while driving
Most Common Causes
- 1
Open or shorted field control wiring
The wire connecting the PCM to the alternator field terminal is broken, corroded, or shorted to ground. This is the most common cause and prevents the PCM from controlling alternator output.
- 2
Defective alternator
Internal alternator failure such as a faulty field winding, damaged voltage regulator, or failed diode bridge prevents proper charging. Testing with a dedicated alternator tester confirms this.
- 3
Blown fuse or fusible link
The alternator field circuit fuse or fusible link has opened, cutting power to the field control circuit. Check the fuse panel for a blown 10-15 amp fuse related to charging.
- 4
PCM programming error or failure
Outdated or corrupted PCM software fails to properly command the alternator field, or internal PCM circuitry controlling the field output has failed.
How to Diagnose It
- 1
Check Open or shorted field control wiring — The wire connecting the PCM to the alternator field terminal is broken, corroded, or shorted to ground. This is the most common cause and prevents the PCM from controlling alternator output.
- 2
Check Defective alternator — Internal alternator failure such as a faulty field winding, damaged voltage regulator, or failed diode bridge prevents proper charging. Testing with a dedicated alternator tester confirms this.
- 3
Check Blown fuse or fusible link — The alternator field circuit fuse or fusible link has opened, cutting power to the field control circuit. Check the fuse panel for a blown 10-15 amp fuse related to charging.
- 4
Check PCM programming error or failure — Outdated or corrupted PCM software fails to properly command the alternator field, or internal PCM circuitry controlling the field output has failed.
How to Fix It
- 1
Inspect and repair field control wiring
Visually inspect the alternator field wire (F terminal) from the PCM to the alternator for corrosion, damage, or loose connections. Use a digital multimeter to test for continuity and proper voltage. Repair or replace damaged wiring as needed.
- 2
Test alternator output
Use a battery/alternator tester or multimeter to measure alternator output voltage at idle (should be 13.5-14.5V) and at 2000 RPM (should be 14-14.5V). If output is low or absent, replace the alternator.
- 3
Check and replace fuses
Locate the alternator field circuit fuse in the fuse panel (consult vehicle service manual for location). If blown, replace with the correct amperage fuse. If it blows again immediately, address the underlying short circuit.
- 4
Update or reprogram PCM
Contact a dealer or qualified programmer to check for available PCM software updates. If a programming error is suspected or confirmed, reprogram the PCM with the latest factory calibration.
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