System Description

Alternative Fuel (AF) fuel pump relay coil is supplied power when ignition is in RUN and START position. Alternative Fuels Engine Control Module (AF ECM) supplies ground path to AF fuel pump relay coil when engine starts and runs on CNG. The purpose of AF fuel pump relay circuitry is to allow AF ECM the ability to turn OFF gasoline fuel pump and to supply a voltage source for lock-off relay. At initial ignition ON, AF fuel pump relay is not energized by AF ECM. The gasoline Powertrain Control Module (PCM) energizes gasoline fuel pump relay, supplying power to Fuel Pump Relay Control circuit for a 2 second prime pulse. When prime pulse is supplied to Fuel Pump Relay Control circuit, lock-off relay is energized and gasoline fuel pump relay receives the 2 second prime pulse power. The 2 second prime pulse is for gasoline fuel pump durability purposes. When engine is operating on CNG, AF ECM energizes AF fuel pump relay in order to turn OFF gasoline fuel pump. The lock-off relay continues to be energized by PCM gasoline Fuel Pump Relay Control circuit.