Engine Controls Schematic Icons
Engine Controls Schematic Icons Icon Icon Definition NOTE: The OBD II symbol is used on the circuit diagrams in order to alert the technician that the circuit is essential for proper OBD II emission control circuit operation. Any circuit which fails and causes the malfunction indicator lamp (MIL) to turn ON, or causes emissions-related component damage, is identified as an OBD II circuit
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Fuel Injector Control Module Description
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.
Fuel System Operation
This vehicles primary fuel source is compressed natural gas (CNG). The vehicle will only switch-over to gasoline operation if one of the following conditions is present
- The fuel tank pressure sensor indicates CNG fuel pressure is below 1,379 kPa (200 psi).
- Every 100th start the vehicle will start and run briefly on gasoline. After this, a switch-over to CNG will occur during the first decel condition.
- A system fault is detected by the PCM.
- The engine cranks for 8 seconds and fails to start on CNG.
Fuel Gage Operation
The CNG fuel level is determined by the PCM. The PCM monitors the FTP and FTT sensors that are located on the CNG tank high pressure lock-off solenoids. The PCM performs a calculation of the CNG pressure and CNG temperature in order to determine an accurate CNG fuel level. The gasoline fuel level is determined by the PCM in a conventional manner using an in-tank variable resistor sensor. Under normal conditions the instrument panel fuel gage displays the level of fuel that the vehicle is operating on. A fuel gage selector switch allows the two different fuel system tank levels to be displayed by the one instrument panel fuel gage. The fuel gage selector switch is a momentary-closed type switch located to the right of the instrument panel. The fuel gage switch allows the vehicle operator to observe the fuel level of the non-operating fuel system. The PCM monitors the status of the switch. When the switch is pressed, the PCM changes the fuel level signal to display the non-operating system fuel level. Once requested, the non-operating fuel system level will be displayed for about 10 seconds. The PCM communicates fuel level to the instrument panel fuel gage through serial data.