Faulty or drifting fuel rail pressure sensor; Low fuel pressure from a weak fuel pump or in-tank lift pump; Blocked or restricted fuel filter; Wiring or connector fault in the sensor supply, ground or signal circuit (damage, corrosion, high resistance); Faulty fuel pressure regulator or pressure control valve, or a leaking injector affecting rail pressure (depends on engine type); Fuel leak or air in the fuel system; Fault inside the engine control unit.

P0191

Fuel Rail Pressure Sensor Circuit Range/Performance Bank 1.

Generic
Powertrain
Generic code
Medium severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
1: AreaFuel and air metering
91: FaultThe specific fault in that area

What it means

P0191 is the generic code for a range or performance fault in the fuel rail pressure sensor circuit. The engine control unit has seen a reading from the sensor that does not make sense, for example a value that does not match the commanded pressure, is stuck, or does not move as expected with engine load and speed. The code does not say whether the sensor itself or the fuel system it measures is at fault. The layout and the pressure involved depend on the engine, so check the manufacturer data for your model.

Symptoms

Malfunction indicator lamp on
Hard starting or long cranking
Rough idle or hesitation under load
Loss of power or limp mode
Intermittent stalling
Poor fuel economy

Possible causes

Faulty or drifting fuel rail pressure sensorlikely
Low fuel pressure from a weak fuel pump or in-tank lift pumplikely
Blocked or restricted fuel filterlikely
Wiring or connector fault in the sensor supply, ground or signal circuit (damage, corrosion, high resistance)possible
Faulty fuel pressure regulator or pressure control valve, or a leaking injector affecting rail pressure (depends on engine type)possible
Fuel leak or air in the fuel systempossible
Fault inside the engine control unitrare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting engine speed, load and rail pressure at the time the code set
Check for other fuel, injector or sensor supply voltage codes that could point to a shared cause
Visually inspect the sensor, its connector and wiring for damage, chafing, corrosion, fuel contamination and leaks
Check the fuel level and quality, and the service history of the fuel filter
With a scan tool, compare actual and desired rail pressure at key on, idle and under load, and check the sensor reading does not move with the engine off
Measure the sensor supply voltage, ground and signal voltage against the manufacturer specification
Test fuel delivery pressure and volume, including the lift pump and regulator or pressure control valve, using the procedure for your engine
Check for leaking injectors or air in the fuel system as the engine type requires

How to fix

Replace the fuel rail pressure sensor if its readings are wrong or stuck and the circuit tests good
Repair or replace damaged wiring and clean or replace faulty connector terminals
Replace the fuel filter if blocked or overdue for service
Replace a weak fuel pump or a faulty pressure regulator or control valve
Repair fuel leaks and bleed the system if air is present
Clear the code after repair and road test to confirm it does not return

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but it may lose power, stall or go into limp mode. Get it checked soon, as low fuel pressure can cause engine damage or leave you stranded.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.