Conditions For Setting DTC
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2002 Pontiac Grand Prix, 2002 Pontiac Bonneville, 2002 Chevrolet Monte Carlo, 2002 Chevrolet Impala, and 2002 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
DTC sets when generator turn on signal circuit voltage is low while PCM is commanding generator on for more than 30 seconds; or when generator field duty cycle signal PWM is less than 5 percent and engine RPM is less than 2500 for more than 30 seconds.