The fuel injector control module (FICM) is a non-flashable control module that is not capable of serial data communication.
The FICM performs the following tasks:
| • | Operates the CNG injectors based upon the powertrain control module (PCM) injector signals |
| • | Supplies the reference, ground and signal circuits to the fuel rail temperature (FRT), fuel tank pressure (FTP) and fuel tank temperature (FTT) sensors |
| • | Communicates the FRT, FTP and FTT sensor values to the PCM using a single dedicated PWM circuit |
| • | Communicates FICM diagnostic information to the PCM using a dedicated PWM circuit |
The PCM controls fuel delivery and determines fuel system operation. The PCM monitors various engine and vehicle functions to provide the correct amount of CNG or gasoline fuel under all operating conditions. The fuel injector control circuits, an AF enable circuit and 2 PWM communication circuits connect the PCM to the FICM. The PCM is not capable of operating the high current CNG fuel injectors. The PCM injector pulse width signals are received by the FICM and duplicate pulse width signals are generated by the FICM in order to operate the CNG injectors. The Bi-fuel vehicles utilize underhood mounted injector relays. When operating on gasoline the injector relays are energized allowing the PCM injector pulse width to go directly to the gasoline injectors.
Fuel Mode Operation
The PCM opens the AF enable circuit when operating on CNG. When the AF enable circuit is open the FICM will operate the CNG injectors based upon the PCM pulse width signals. The FICM will convert the FRT, FTP and FTT sensors voltage signals to PWM signals that the PCM monitors for fuel trim and fuel gage adjustment. The PCM also monitors the FICM status signal circuit for proper FICM operation.
Communication Circuits
Sensor PWM Circuit
The FRT sensor information is required by the PCM for fuel trim adjustment. The FTP and FTT sensors information is required by the PCM for fuel gage operation. The PCM does not have the ability to supply and monitor the FRT, FTP and FTT sensors. The FICM performs this task by supplying the sensors a 5-volt reference, low reference and signal circuit. The signal voltage of the sensors are converted into a PWM signal. The PWM signal is sent to the PCM through a dedicated circuit. The PCM converts the PWM signal into pressure and temperature values.
FICM Diagnostic Circuit
The PCM monitors the FICM diagnostic circuit in order to set FICM related DTCs. The FICM diagnostic circuit is a 5-volt circuit that is pulse width modulated by the FICM in order to communicate diagnostic information to the PCM.
