P0622Generator Field/F Terminal Circuit
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- How the car detects it
- The alternator regulator is linked to the engine module by an L (turn-on) line, an F (field) line reporting field load as a duty cycle, or on newer cars a LIN bus. P0622 checks the F feedback: its duty cycle equals the field on-time, from which the module calculates alternator torque and raises idle under load. Two plausibility tests: with ignition on and engine off the duty cycle must be near 0 % – a fault at 65 % or more; with the engine running (below 3000 rpm) it must be 5–99 % – a fault at 5 % or less. GM's 2023 and 2025 modules use 5 s each and, unusually, set the check engine light in the first trip; the Saab 9-4X uses 5 s and 15 s without it and only when P0621 is not set. Other systems split the same check into P0625 (low) and P0626 (high).
- What you may notice
- Battery warning lamp on
- Check engine light possible on GM from model year 2023
- Idle fluctuates or drops when large loads switch on
- Flat battery with a real charging fault
- Likely causes
- LikelyF line or alternator connector open or shorted
- LikelyRegulator or alternator faulty (field driver)
- PossibleAlternator not charging (belt, brushes), duty cycle implausible
- RareModule or software
- Repair
- Medium · Usually a job for a workshop.Typical cost: €30 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.