* Ignition On, Engine Off: When you turn the ignition key to the "on" position (but before starting the engine), you'll hear the fuel pump run for a few seconds. This is a prime cycle. Its purpose is to pressurize the fuel lines and ensure there's fuel ready to be injected into the engine the moment you crank it. This is a normal and necessary function.
* Engine Running: The fuel pump runs continuously while the engine is running. It's constantly supplying fuel at a pressure needed to meet the engine's demands, varying with the throttle position (how hard you're accelerating).
* Other Potential Reasons (less common, often indicating a problem):
* Faulty Fuel Pump Relay: This relay acts as a switch for the pump. A malfunctioning relay might cause the pump to run intermittently or not at all.
* Low Fuel Level: While not a direct cause of *the pump itself* coming on, a very low fuel level might trigger the pump to work harder, causing it to be more noticeable.
* Fuel Pump Issues: A failing fuel pump might make more noise or run intermittently, potentially leading you to notice it more. A failing pump will eventually stop supplying sufficient fuel.
* Computer Issues (PCM): The Powertrain Control Module (PCM) monitors various engine parameters and controls the fuel pump. A problem with the PCM could lead to incorrect fuel pump operation.
In short, hearing the fuel pump is normal when you turn the ignition on and while the engine is running. If you hear unusual noises, the pump runs constantly even with the ignition off, or the vehicle won't start, it indicates a potential problem requiring attention.
