As a car sits, the fuel pressure gradually decreases and modern cars don’t run without fuel pressure. The PCM will ground the fuel pump relay which supplies power to the fuel pump under some specific circumstances. Which method utilized is entirely dependant on the manufacturer, and they are constantly coming up with creative ways to revolutionize these systems. These sensors are used in a variety of ways.
Other options are crank sensors and/or cam sensors. There won’t be any reference pulses if the motor is not turning. Some monitor reference pulses from the ignition module. Each manufacturer will use a different indicator that the motor is running. It is the primary component that allows our modern vehicles to run smoothly and efficiently. The PCM monitors all signals in the engine compartment. How does the PCM know the engine is running? If the PCM doesn’t see an indication of the motor running, it will not supply a ground path to the relay and the fuel pump will not receive power. The PCM chooses to turn the relay on when it sees the motor is running. The fuel pump relay is controlled by the PCM by providing the relay with a ground. They are entirely dependant on the fuel pump relay to provide them with power or remove their power. Fuel pumps themselves don’t know when to shut off. The are two main components that make most fuel pumps run: the PCM (Powertrain Control Module) and the fuel pump relay.