DTC P1209: Fuel Injector Control Module PWM Output Signal Failure: Description
WARNING: This page is about a different car, the 2003 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
The Fuel Injector Control Module (FICM) monitors the CNG fuel injector circuits. The CNG fuel injector circuit status and internal FICM diagnostic data, is communicated to the Powertrain Control Module (PCM) by a Pulse Width Modulated (PWM) circuit. This DTC sets when the FICM diagnostic output PWM signal is not received by the PCM.