The PCM controls fuel delivery and for KL6 vehicles, determines which fuel system the engine is operating on. The PCM monitors various engine and vehicle functions to provide the correct amount of CNG or gasoline fuel under all operating conditions. This provides excellent driveability and fuel economy while maintaining reduced emission levels. When operating on CNG, the PCM grounds the AFO enable circuit. When the AFO enable circuit is grounded, the fuel injector control module (FICM) will sequentially operate the CNG fuel injectors. 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 PCM monitors PWM signals from the FICM in order to determine CNG fuel rail pressure (w/o JL4), CNG fuel rail temperature, and the diagnostic status of the FICM. The FICM monitors the CNG fuel rail pressure sensor (w/o JL4), and the CNG fuel rail temperature sensor. This information is communicated to the PCM by dedicated PWM circuits. The FICM also performs internal diagnostics, and communicates this information by a dedicated PWM circuit. For further detail refer to Fuel Injector Control Module Description .

The PCM controls the Low Pressure Lock-Off (LPL) solenoids, and the High Pressure Lock-Off (HPL) solenoids. The PCM commands the HPL solenoids open for 1 second at every ignition ON, in order to prime the CNG fuel system. The PCM commands the HPLs, and the LPL open, when the engine is cranking or running on CNG.

When operating on gasoline, the PCM will turn the fuel indicator lamp ON. The fuel indicator lamp (FIL) is located within the headlamp switch assembly near the fuel gage select switch. The FIL is also turned ON for a two-second bulb check whenever the ignition is turned ON. The fuel gage select switch allows the vehicle operator the ability to request fuel gage display of either fuel tank.

The PCM also determines the CNG fuel level. 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.

For further PCM description refer to Powertrain Control Module Description in Engine Controls in the G/H Van Service Manual.