Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Circuit Description
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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.