Communication Circuits
WARNING: This page is about a different car, the 2003 Pontiac Sunfire, 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, and 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
The PCM monitors the FICM diagnostic circuit to set FICM related DTCs. The FICM diagnostic circuit is a 5 volt circuit that is pulse width modulated by the FICM to communicate diagnostic information to the PCM.