A P0625 code in your 2022 Cadillac XT5 indicates that the ECM has detected low voltage on the generator field terminal circuit. This circuit controls the alternator's output by regulating the field winding current. Low voltage here suggests the circuit is shorted to ground or has other issues preventing normal operation.
Field Terminal Circuit Function
Your XT5's alternator output is controlled by varying the current through its field winding. The ECM adjusts this field current to match electrical demand and optimize fuel efficiency. The field terminal circuit carries the control signal from the ECM to the alternator. When this circuit shows low voltage, proper control is compromised.
What Causes Low Field Terminal Voltage
A short to ground in the field terminal wiring is the primary cause. This could be from chafed insulation, pinched wires, or water intrusion causing ground paths. Corroded connectors with internal moisture paths act like shorts. An internal alternator failure may create a ground fault within the unit. The ECM's field control driver may have failed in a shorted condition.
Symptoms in Your XT5
Charging may be erratic—sometimes too high, sometimes too low. The battery warning light typically illuminates. You might notice electrical system instability or battery discharge. The ECM may enter a default charging mode that doesn't optimize for fuel economy.
Cadillac-Specific Diagnosis
Using GM GDS2, monitor field control commands and actual field circuit voltage. The system should show the ECM commanding different duty cycles and the field responding appropriately. Check for voltage at the field terminal connector with the alternator disconnected to isolate alternator versus wiring issues. Inspect the wiring harness routing for potential ground contact points.