P1638moderate severityPowertrain
Generator F-Terminal Circuit
on 2005 Cadillac CTS 2.8L V6 · RWD
What this code means
The PCM detected a fault on the generator (alternator) F-terminal (field) circuit. The F-terminal circuit controls the generator field current to regulate charging voltage.
Symptoms
- Battery light on
- Overcharging or undercharging
- Battery damage from overcharging
- Dim lights
Common causes
- Faulty generator/alternator
- F-terminal wiring damage
- PCM control driver failure
- Corroded connector
Diagnostic steps
- Test generator field voltage
- Inspect F-terminal wiring
- Test generator output regulation
- Check PCM field control signal
Repair notes
Test and replace generator if field control is faulty. Inspect wiring.
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