P0625
Generator Field Terminal Circuit Low
Powertrain Engine Cooling Charging System 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Your alternator's field circuit isn't getting enough electrical signal from the engine computer, like a dimmer switch stuck too low. This prevents the alternator from charging your battery properly.

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Symptoms You May Notice
3 known symptoms for this code
Battery warning light on dashboard
Dim headlights or interior lights
Battery drains quickly or vehicle won't start
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECM monitors voltage on the alternator's field terminal, which controls how much the alternator charges. When this voltage drops below the minimum threshold (typically 0.5V), the ECU detects a low field signal and sets the fault code. This indicates a wiring break, connector issue, or internal ECM problem preventing proper field control.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Field Terminal Voltage 5-12V during charging Below 0.5V
Charging System Output 13.5-14.5V at idle Below 12.5V
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Alternator field wiring harness
Inspect connector at alternator for corrosion, loose pins, or damaged wire and clean or reseat as needed.
2
Alternator field wire
Test continuity from ECM to alternator field terminal with multimeter; repair or replace broken wire if found.
3
Alternator assembly
Replace alternator if wiring tests good but voltage remains low, indicating internal field coil failure.