The fuel rail pressure sensor keeps the powertrain control module (PCM) aware of the pressure levels in the fuel rail, so that the computer knows how much fuel the engine needs. When the PCM receives an irrational signal from the fuel rail pressure sensor, the module logs the P0191 code.
What Does the P0191 Code Mean?
Diagnostic trouble code (DTC) P0191 stands for “Fuel Rail Pressure Sensor Circuit “A” Range/Performance.” It indicates a potential abnormality in the fuel rail pressure readings. Because of either a mechanical or electrical problem, the signal sent by the fuel rail pressure sensor doesn’t match the value the PCM expects to see.
Typically a “performance” code like P0191 is related to one of the ECM/PCM’s rationality checks; meaning, that the measured value doesn’t line up with what the ECM/PCM expects to see based on other inputs pertinent to the value being measured.
Too little fuel will reduce the engine’s output when conditions demand all the power it can get. Conversely, adding more fuel than the engine could combust will waste fuel and raise emission levels in the engine exhaust, potentially causing damage to the catalytic converter.
To prevent both lean and rich mixtures from compromising the engine’s performance, the PCM regulates the output of the fuel injectors to add the right amount of fuel to the engine. On many modern vehicles, the PCM depends on the fuel rail pressure sensor to send it a constant stream of accurate data and will log the P0191 code if it gets the wrong signals from the sensor.
A technical knowledge of common rail fuel injection systems could help you address P0191 if you’re planning a DIY fix. You can read our in-depth explanation here.
Note: The Society of Automotive Engineers (SAE) defined the generic code P0191. But the vehicle’s manufacturer may define the trouble code differently.
What are the Possible Causes of the P0191 Code?
Several mechanical and electrical issues can trigger the P0191 code. They include:
- Bad or failing fuel pressure sensor
- An issue with the fuel pressure sensor circuit
- Fuel pressure that’s too high or too low
- An issue with the PCM, such as software in need of an update
What are the Common Symptoms of the Code P0191?
Since the code P0191 concerns the engine’s fuel supply, its effects are typically noticeable. Likely warning signs of a problem with the fuel rail pressure sensor and its circuit include:
- Check Engine Light triggers or blinks
- Increased fuel consumption
- Abnormal smell in the tailpipe emissions
- Engine hesitates or stalls
- PCM logged a rich fuel trim code (P0172 Code: Fuel system too rich)
- PCM logged a lean fuel trim code (P0171 Code: Fuel system too lean)
- Failed emissions test
Very rarely, a vehicle will not display any warning signs associated with a PO0191 code. You can check the PCM by plugging your OBD-II scanning tool into the right port and checking the diagnostic trouble codes logged by the computer.
How to Diagnose the P0191 Code
Only car owners who possess sufficient skills and experience in DIY auto repair should try their hand at fixing a P0191 code. Those who lack confidence or time should bring their vehicle to a reliable auto repair shop for diagnosis and repair.
Learn how to diagnose a P0191 Ford case with the video below. Even if your vehicle is of a different make or model, watching the video can give you a better idea about checking the fuel rail pressure sensor and its circuit.
How to Fix the P0191 Code
Once you’ve established what triggered the P0191 code, figure out how to fix it. Rely on credible online resources. Make sure that the fix you find is specific to your vehicle’s make and model. Consider investing in an ALLDATA subscription for comprehensive repair guides that will help you resolve this DTC and other issues you may encounter in the future.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.