P0231 indicates the powertrain control module (PCM) has detected low voltage on the secondary fuel pump control circuit. This circuit is typically the low-side driver or feedback/monitor side of the fuel pump relay or fuel pump driver module. The code is set when the monitored signal falls below a calibrated threshold for a set period of time.
Worn relay contacts or a failed relay coil can prevent the fuel pump from receiving proper voltage, producing a low-circuit signal. This is one of the most common and inexpensive causes.
Chafed insulation, broken wires, or corroded pins in the fuel pump or relay connectors create high resistance or intermittent open circuits, leading to a low-voltage reading.
A worn pump motor draws excessive current or has increased resistance, which can pull the monitored circuit voltage below spec. Often accompanied by low fuel pressure.
On vehicles that use a separate driver module or dropping resistor to control pump speed, an internal failure in this component can cause the secondary circuit to read low.
A loose, rusty, or broken ground strap or ground wire creates a high-resistance path, which the PCM interprets as a low-circuit fault.
A failed internal transistor in the PCM that controls the fuel pump relay or driver is rare but possible. This should be considered only after all other causes have been ruled out by direct testing.
Almost never. Although online sources sometimes suggest the PCM, in real-world cases P0231 is far more often caused by the fuel pump relay, wiring, the pump itself, or the driver module. The PCM should only be replaced after all other components have been directly tested and confirmed good.
It is not recommended. The code indicates a real fault in the fuel pump control circuit, and the engine may stall without warning, leaving you stranded or creating a safety hazard.
Not always. The relay and wiring problems are generally more common than a failed pump. A failing pump is more likely if the code is accompanied by confirmed low fuel pressure or whining noises from the tank.
Not directly. P0231 is an electrical code about a low-voltage reading on the control circuit. However, because the underlying fault can prevent the pump from running properly, low fuel pressure is often a downstream symptom that should still be verified with a gauge.