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.
System Description
The lock-off relay coil is supplied power whenever Powertrain Control Module (PCM) energizes gasoline fuel pump relay. When lock-off relay is energized, it supplies power to High Pressure Lock-Off (HPL) solenoid and Low Pressure Lock-Off (LPL) solenoid. At initial ignition ON, PCM energizes gasoline fuel pump relay Control circuit, which supplies power to fuel pump power circuit for a 2 second prime pulse. At initial ignition ON, Alternative Fuels Engine Control Module (AF ECM) will close HPL Control circuit, completing circuit path to ground, to allow for a 2 second CNG prime pulse. The prime pulse occurs at the same time as gasoline fuel pump prime pulse occurs. PCM will supply power to fuel pump relay Control circuit regardless of fuel system that is in operation as long as crankshaft pulses are received.
NO RELATED
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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.