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
- internally routes the powertrain control module (PCM) injector control circuits to the CNG injector drivers or the gasoline injectors (KL6 only)
- operates the CNG injectors based upon the PCM injector signals
- supplies the reference, ground and signal circuits to the fuel rail pressure (FRP) and fuel rail temperature (FRT) sensors
- communicates the FRP sensor values to the PCM using a dedicated PWM circuit
- communicates the FRT sensor values to the PCM using a dedicated PWM circuit
- communicates FICM, FRP and FRT diagnostic information to the PCM using a dedicated PWM circuit
The PCM controls fuel delivery and determines fuel system operation on Bi-fuel (KL6) equipped vehicles. 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 3 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. KL6 equipped vehicles utilize a FICM that contains internal relays. When operating on gasoline the internal relays allow the PCM injector pulse width to go directly to the gasoline injectors.
Fuel Mode Operation (KL6 and KL8)
The PCM grounds the AF Enable circuit when operating on CNG. When the AF Enable circuit is grounded the FICM will operate the CNG injectors based upon the PCM pulse width signals. The FICM will convert the FRP and FRT sensors voltage signals to independent PWM signals that the PCM monitors for fuel trim adjustment. The PCM also monitors the FICM Diagnostic Input circuit for proper FICM operation.
KL6 Operation
When gasoline operation is desired the PCM opens the AF Enable circuit. Switchover from one fuel to the other is always performed in an orderly, sequential manner. Since some injectors are in the middle of injecting the previous fuel, the FICM will wait until that cylinders fuel delivery is complete and will then switch over in sequential firing order.
Fuel Gauge Operation
The CNG fuel level is determined by the PCM. The PCM monitors the FTP and FTT sensors that are located on one of 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. On Bi-fuel (KL6) models the gasoline fuel level is determined by the PCM in a conventional manner using an in-tank variable resistor sensor.
Bi-Fuel (KL6) Fuel Gauge Operation
Under normal conditions the instrument panel fuel gauge displays the level of fuel that the vehicle is operating on. A fuel gauge selector switch allows the two different fuel system tank levels to be displayed by the one instrument panel fuel gauge. The fuel gauge selector switch is a momentary-closed type switch located within the headlamp switch assembly. The fuel gauge 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 depressed 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 gauge through serial data.
Dedicated CNG (KL8) Fuel System Operation
The dedicated CNG fuel system operation is functionally the same as the bi-fuel CNG fuel system. The vehicle does not contain any gasoline fuel system components. A third CNG fuel tank is placed in the location of the frame mounted gasoline fuel tank. The vehicle does utilize a PCM that operates in conjunction with the FICM. The calibration programmed into the PCM has disabled the gasoline specific DTCs. The PCM still performs diagnostics on the vehicle sensors such as ECT, TP, IAT, etc.