P0622 — Generator Field F Terminal Circuit
What it means: Generator Field F Terminal Circuit.
How serious / can you keep driving: Serious. Power derate likely — plan to stop soon.
Check first: Test field circuit resistance
Don't risk it — look up listed providers near you and give them this code when you call.
Listed providers nearest Billings, MT
Closest first. Tell them P0622 and what the truck is doing. RoadService.app lists these providers and does not employ them or carry out the repair.
- 0.0 mi away — based in Billings, MT · (406) 245-8985
- 0.0 mi away — based in Billings, MT · (406) 252-8413
- 0.0 mi away — based in Billings, MT · (406) 780-3711
Seen on: Heavy Truck
What P0622 means
Generator Field F Terminal Circuit. Common causes: Alternator field circuit fault.
How serious is it?
Serious. Power derate likely — plan to stop soon.
Most likely causes
- Alternator field circuit fault
- Failed voltage regulator
- open field circuit
First moves (roadside)
- Test field circuit resistance
- replace alternator if field open
FAQ
Generator Field F Terminal Circuit. Common causes: Alternator field circuit fault.
Serious — Power derate likely — plan to stop soon.
The most common cause is: Alternator field circuit fault. Other possibilities include Failed voltage regulator; open field circuit.
Power derate likely — plan to stop soon. When in doubt, get a qualified mobile diesel tech on the truck before continuing.
Related codes
Codes that commonly appear alongside P0622, or share the same subsystem.
- ECU Power Supply — Intermittent / Erratic (SPN 627 FMI 2)
- Battery / Charging Voltage — Low (SPN 168 FMI 18)
- Engine Controller (ECM) — Internal Fault (SPN 629 FMI 12)
- Battery voltage low during crank (SPN 168 FMI 17)
- J1939 proprietary datalink lost (SPN 625 FMI 9)
- J1939 Data Link — Communication Error (SPN 639 FMI 2)
- High Speed CAN Bus Fault (U0001)
- Lost Communication with ECM/PCM (U0100)
Same symptom: Charging and voltage
Other codes that trace back to voltage — one bad ground can set half a dozen of them at once.
- System Voltage Malfunction (P0560) · Electrical, Charging & Network
- System Voltage Low (P0562) · Electrical, Charging & Network
- System Voltage High (P0563) · Electrical, Charging & Network
- Starter Relay Circuit High (P0619) · Electrical, Charging & Network
- Generator Control Circuit (P0620) · Electrical, Charging & Network
- Generator Field Terminal Circuit Low (P0625) · Electrical, Charging & Network
Find a mechanic or related guides
General diagnostic guidance for diesel engines (Cummins, Detroit, PACCAR, Volvo, Mack and more). Not a substitute for a scan-tool diagnosis on your specific truck.