P0191 trouble code definition
Fuel Rail Pressure Sensor Circuit Range/Performance is the technical definition for this code
Note: This code may be associated with:
- OBD-II Trouble Code P0171 (excessively rich fuel system)
- OBD-II Trouble Code P0172 (excessively lean fuel system)
What the P0191 code means
The power control module (PCM) regulates the amount of fuel that is released into the combustion chambers by controlling the fuel injectors. This process works to reduce tailpipe emissions. In order to work effectively, the power control module must always know what the fuel pressure is. If the fuel rail pressure sensor is giving inconsistent readings, the power control module (PCM) will store the P0191 trouble code.
What causes the P0191 code?
- Faulty fuel pressure sensor
- Faulty fuel pressure sensor circuit
- Faulty fuel pressure sensor connector
- Faulty fuel pressure regulator
What are the symptoms of the P0191 code?
- Check Engine Light on
- Decrease in fuel economy
- Engine may be stalling or hesitation
- Engine may cut off when the vehicle stops
- Unusual smell emitting from the tail pipe
- No noticeable symptoms
- Trouble codes P0171 and/or P0172 stored in the power control module
How does a mechanic diagnose the P0191 code?
The mechanic will use the OBD-II scanner to retrieve the freeze frame data to find out what the condition of the vehicle was when trouble code P0191 was set by the power control module (PCM).
Completes a test drive and uses the live data to determine whether the fuel pressure reading is normal.
Uses a fuel pressure tester to make a determination as to whether there is a sensor problem or a fuel pressure problem.
If the fuel pressure is normal, they will use an oscilloscope to test the connector and wiring of the fuel rail pressure sensor. The purpose of this is to confirm that the sensor’s circuitry is unimpaired.
The sensor is most likely defective if the actual fuel pressure is normal and the sensor’s circuitry is unimpaired.
Common mistakes when diagnosing the P0191 code
A common mistake when diagnosing the P0191 trouble code is overlooking the other components that may need to be repaired and replacing the fuel rail pressure sensor first.
Wiring that is insufficiently connected or chafed, a faulty fuel pressure regulator or faulty fuel pump are things that are often missed when doing a diagnosis and completing a repair.
How serious is the P0191 code?
The P0191 trouble code is considered serious as it is known to cause drivability issues. Operating a vehicle while this code is present could cause the car to stall out or hesitate while driving. There may also be an increase in fuel consumption, which can be costly. It is important to take this code seriously and have it diagnosed and repaired as soon as possible.
What repairs can fix the P0191 code?
- Replacing the fuel pump
- Replacing the fuel pressure regulator
- Repairing any broken, frayed, or shorted wires that lead to the fuel pressure sensor
- Repairing corroded connector to the fuel pressure sensor
- Replacing fuel pressure sensor
- Repairing any vacuum leaks in the engine
Additional comments for consideration regarding the P0191 code
Most of the time, there are other components that cause this trouble code. Take your time and consider all of the possibilities before concluding that the fuel rail pressure sensor is faulty. Also, make sure you have the proper tools necessary for diagnosis. You will need an OBD-II scanner and an oscilloscope.
Need help with a P0191 code?
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