Circuit Description

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CNG vehicles have 2 modes, gasoline and Natural Gas Operation (NGO). Vehicle operates on CNG except during the following conditions:

Fuel pressure sensor indicates CNG tank is empty.
A wide-open Mixture Control Valve (MCV) is detected.
AF ECU detects a system fault. Not all DTCs will cause gasoline operation.
Engine crank time exceeds 8 seconds.
Every 100 starts, vehicle will start and run briefly on gasoline.
When engine coolant temperature is less than 10°F (-12°C), vehicle will start and run briefly on gasoline.
If CNG fuse (20-amp) is removed from underhood fuse block.

Switch to CNG will only take place during deceleration. Under certain heavy load conditions, switch to gasoline may occur. Perform system diagnosis to verify system pressure is sufficient. See FUEL SYSTEM DIAGNOSIS (ALTERNATIVE FUEL) . Fuel Indicator Light (FIL), located on fuel gauge select switch will illuminate during gasoline operation.