Theory Of Operation

WARNING: This page is about a different car, the 2013 RAM 2500 HD and 2012 RAM Pickup. However, it is still accessible from the selected car via links, so may be relevant.

There are two unique Fuel Injector Relay assemblies that supply voltage to the CNG and gasoline Fuel Injectors. When the ambient temperature and engine is cold, the vehicle will start out in gasoline fuel mode. During this time, the Powertrain Control Module (PCM) will close the low side driver for the control circuit on the gasoline relay providing a constant 12 volts to the gasoline Fuel Injectors. When the PCM makes the determination to switch to CNG fuel mode, it will open the low side driver to the control circuit on the gasoline relay and close the low side driver for the control circuit on the relay providing a constant 12 volts to the CNG Fuel Injectors. The injectors are controlled on the ground side by the low side drivers inside the PCM. The Fuel Injector Control circuits for both fuel systems injectors are spliced together and controlled by the same low side driver circuit. For example; both Fuel Injector 1 Control circuits are connected to the Fuel Injector Control circuit at the PCM. The PCM will control the pulse width on the control circuit depending on which mode of operation the vehicle is in. The pulse width will typically be much longer when in CNG fuel mode as compared to gasoline fuel mode.