What does it mean?
The internal combustion engine needs three basic things to start and run: air, fuel, and spark. With regards to this DTC (diagnostic trouble code), we’ll be focusing on fuel. The fuel system includes the fuel tank, a low-pressure fuel pump, sometimes a high-pressure fuel pump, fuel tubes and hoses, a fuel pressure regulator, and the fuel injectors. The fuel pump and fuel injectors are operated electrically and electronically, so there are also fuses, relays, and a controller for these.
Usually, the controller is part of the ECM (engine control module), though some vehicles, such as some diesels, may have a separate fuel injector driver module. Usually, the fuel pump relay is commanded by the ECM. The ECM grounds the fuel pump relay control or primary circuit, which then feeds power to the fuel pump using the power or secondary circuit. On some vehicles, turning the key on will turn the pump, on for a few seconds, to prime the system.
If the ECM detects crank but not engine starting, using the RPM signal from the crank position sensor, it will turn off the fuel pump after a set period. To ensure proper fuel system function, everything needs to work in concert. If there is insufficient fuel pressure, the fuel injectors won’t be able to deliver fuel properly, for example. Insufficient fuel pressure can be caused by any number of electrical problems, one of which is poor voltage to the fuel pump.
The ECM monitors the fuel pump relay secondary circuit for voltage. If voltage drops below a certain threshold, it will set DTC P0231, which is defined as “Low Voltage Fuel Pump Secondary Circuit.”