What P0622 means
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.
How the engine computer detects it
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).
Written from public technical sources and not yet checked by a mechanic. How we write these pages
Symptoms
- 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
Common causes
- F line or alternator connector open or shorted Most likely
- Regulator or alternator faulty (field driver) Most likely
- Alternator not charging (belt, brushes), duty cycle implausible Possible
- Module or software Less likely
How to diagnose P0622
- Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
- Inspect the parts involved: alternator, voltage regulator, generator wiring, engine control module.
- Work through the causes above from most to least likely, cheapest checks first.
- Clear the code and drive a full drive cycle to confirm the repair held.
Reading the code
- P
- Powertrain
- 0
- Generic (SAE) code
- 6
- Computer and output circuits
- 22
- Specific fault
Questions drivers ask
Can I drive with code P0622?
Only for a short distance. When the charging system isn't working right, the car may run on battery power alone and can stall, sometimes taking power steering with it. Turn off accessories you don't need and head straight to a shop.
This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.