P0622: generator field-feedback duty cycle needs operating context

P0622 is the generator F-terminal circuit integrity monitor in the cited GM examples. The measured quantity shown is generator field-winding duty cycle, not simply charging-system voltage.

A high duty cycle can be wrong in a stopped-engine test

The displayed branch flags duty cycle at or above 65 percent while the engine is not running and no crank movement is detected. It requires generator presence, enabled calibration, run/crank voltage of at least 11 volts and specified crank/cam faults absent. Applying the 65-percent boundary indiscriminately to a running generator would strip away the conditions that make it diagnostic.

The table uses five seconds of accumulated fault time with a fifty-millisecond task rate. The same page begins another branch at or below five percent, but its complete conditions continue beyond the displayed extract; no universal two-sided normal duty-cycle range is asserted here.

Useful verification

Capture the duty-cycle signal together with engine state and diagnostic status. A plausible battery voltage cannot by itself establish that the F-terminal feedback signal is valid. Equally, this code alone does not prove insufficient generator output or prescribe replacement.

After the applicable service procedure resolves the cause, verify the relevant enabled F-terminal diagnostic and charging-system operation as required for that vehicle. The two cited pages agree on the shown stopped-engine branch and classify the diagnostic as Type A over one trip. Their file-level coverage is not proof of applicability to every generator architecture.

Source and applicability

Documented monitors in gm-2025-03a, gm-2025-04b, model year 2025. These are module/calibration examples; vehicle, engine and transmission applicability must be confirmed independently. GM 2025-03a, page 408. GM 2025-04b, page 621.