Circuit Description

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Savana, 2003 Chevrolet Silverado, and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

The PCM controls the fuel system while the vehicle is operating on CNG. A High Pressure Lock-Off (HPL) solenoid in each CNG tank and a Low Pressure Lock-Off (LPL) solenoid in fuel rail prevent fuel flow. The PCM commands ONLY the HPL's open for one second at every ignition on for a CNG prime pulse. The CNG prime pulse is performed in order to charge the fuel line and also allows the Fuel Tank Pressure (FTP) sensor to monitor the amount of fuel pressure in the tanks. The PCM commands both the HPL and LPL open when engine RPM indicates the engine is cranking or running on CNG.

The Alternative Fuel (AF) lock-off relay's coil and switch are supplied power whenever the ignition is in the Start or Run position. The PCM controls the ground path. When the AF lock-off relay is energized, power is supplied to the HPL and LPL solenoids.