P0191 indicates that the engine control module has detected a fuel rail pressure sensor signal that is outside the expected range for Bank 1. This means the sensor, its wiring, or the pressure source is not providing a correct reading.
The sensor itself may be defective, producing an abnormal voltage signal.
Corroded, broken, or poorly connected wires can alter the sensor signal.
A leak or blockage in the fuel rail can cause pressure to fall below the sensor’s expected range.
If the pump or its control valve is not delivering proper pressure, the sensor will read incorrectly.
Rarely, a fault in the engine control module can misinterpret a correct sensor signal, but this is uncommon.
No, the PCM is rarely the cause. The code almost always points to a sensor, wiring, or fuel pressure issue.
It is best to address the code because it can lead to reduced performance or future engine damage if left unresolved.
In most cases it will, but only after confirming the sensor is the source of the fault through proper diagnosis.