If your vehicle has recently had a P0171 trouble code due to a faulty fuel pressure regulator, and you wish to learn how to replace the faulty part without spending hundreds of dollars in the mechanic shop, you are at the right place.
After working on vehicles for over 15 years, I can guide you step by step and help you replace the fuel pressure regulator.
What Is a Fuel Pressure Regulator
A fuel pressure regulator is a device used in modern vehicles designed to maintain proper fuel pressure.
Each vehicle is equipped with a regulator that is preset to maintain fuel pressure for its particular engine.
Inside the regulator housing, there is a spring and a diaphragm. The spring has been preset by the manufacturer for the desired fuel pressure.
The fuel pump has to pump enough fuel with enough pressure to supply fuel to the injectors.
If there is extra fuel, it is sent back to the fuel tank through the fuel return line.
When a vehicle is idle, the fuel pressure is usually around 5 to 10 psi depending on the vehicle.
The high vacuum inside the intake manifold allows the regulator to lower the fuel pressure.
The vacuum signal is sent to the regulator by using a vacuum hose attached directly to the top of the regulator or its side.
To easily locate the fuel pressure regulator, the most common mounting position is at the end of the fuel rail which helps the fuel pressure to remain constant.
The fuel return line allows the excess fuel to travel back to the fuel tank. On most vehicles, the fuel return line is attached next to the regulator.
There is no specific OBD2 trouble code for a malfunctioning fuel pressure because the part itself is a mechanic. However, a faulty fuel pressure regulator can trigger an oxygen sensor code such as P0131, P0135, P0138, P0140, and P2195.
What Is The Correct Fuel Pressure In a Car
The correct fuel pressure in a car is between 35 PSI and 45 PSI. Anything below 35 psi or above 45 psi is considered an incorrect fuel pressure.
The whole point of the fuel system is to maintain constant pressure. Tour fuel injectors work as specific pressure and if that pressure goes up or down then you won’t get a good spray pattern or your engine might run rough or not run at all.
How To Replace The Fuel Pressure Regulator To Fix The P0171 Trouble Code
Here is how to replace the fuel pressure regulator to fix the P0171 trouble code:
1. Disconnect the negative battery terminal
Before working with any electric component of a vehicle, it is important to disconnect the negative battery terminal as any owner’s manual suggests.
This is especially important because you will be working with fuel and you do not need a spark.
2. Locate the fuel pressure regulator
The fuel pressure regulator is located on the end of the fuel rail. Follow the fuel lines from the high-pressure fuel pump (opposite of the fuel filter) and at the end, you will see the fuel pressure regulator.
Since the location of the fuel pressure regulator is not the same on all vehicles, check the owner’s manual for more information.
3. Disconnect the vacuum line/electrical harness
Fuel pressure regulators can have vacuum lines or electrical harness that feeds power to them, depending on the vehicle.
Disconnect the vacuum line/electrical harness and proceed to remove the fuel pressure regulator.
4. Remove the fuel pressure regulator
The fuel pressure regulator is usually held in place by two bolts.
Remove those and slide the bad fuel pressure regulator out of the fuel rail.
5. Install the new fuel pressure regulator
Before you install the new fuel pressure regulator, make sure to oil up the part that goes into the fuel rail.
You will see a rubber o-ring on the fuel pressure regulator. Oil it up using engine oil and slide it to the fuel rail and then install the bolts.
6. Connect the vacuum line/electrical connector
Once everything is back in place, reinstall the vacuum line/electrical connector back in place.
Start the vehicle and see if there is any fuel leaking from the fuel pressure regulator.
7. Erase the P0171 code using an OBD2 scanner
Now that the faulty fuel pressure regulator has been replaced, hook up an OBD2 scanner and read the trouble codes.
When you get a P0171, select it and click erase.
You have now successfully replaced the faulty fuel pressure regulator and fixed the P0171 trouble code.
In Conclusion
Replacing the faulty fuel pressure regulator in order to fix the P0171 trouble code is an easy task that will take up to one hour.
Follow the steps explained above and you will learn how to repair your car.
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