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If you're driving and suddenly your "check engine" light illuminates, and your scanner tool shows the P0191 code, it's essential to know what that means. As we all know, most car problems shouldn't be left unaddressed, and the code P0191 is no exception.
So, what does this code mean? Is this serious? Read on as this blog post will explain everything you need to know about this trouble code and provide some solutions for fixing it.
What is Code P0191?
The P0191 code is a diagnostic trouble code for "Fuel Rail Pressure Sensor Circuit Range/Performance." The Powertrain Control Module (PCM) monitors the fuel pressure to manage the fuel injectors effectively. This also provides the appropriate fuel to the engine's combustion chamber while maintaining the greatest possible power and efficiency.
So, when the PCM detects an issue with the fuel rail pressure sensor or its circuit, specifically a low or high voltage reading, it will throw the P0191 code and illuminate the Check Engine Light.
Symptoms of Code P0191
Fuel pressure has a significant role in how an engine runs. This is designed to give your engine the best possible performance and fuel economy. If the fuel pressure is faulty, it can cause drivability issues. You may experience these common symptoms:
- Hard starts
- Hesitation on acceleration
- Loss of power
- The engine will run lean
Causes of Code P0191
If your car has all those symptoms above, many causes can be the root of your problem. Here are some common reasons:
- High fuel pressure
- Faulty fuel pressure regulator
- Excessive resistance in the circuit
- Vacuum leaks
- No fuel
- Damage wiring and harness
How to Diagnose Error Code P0191?
When determining the exact issue of the P0191 code, a proper diagnosis is required. This ensures that you won't skip any potential causes and save you time and money. However, this is not as easy as you believe!
You need to have at least mechanical skills and knowledge about cars to do it yourself. But since you are reading this guide now, we assume that you are ready to try it! So let's get started!
Check for Other Codes
In troubleshooting, checking for other codes is the best way to start. This is to see if any other codes are associated with the P0191 code. When other trouble codes are present, these will lead you to where you should start diagnosis. If no other codes are found, you may proceed to visual inspection.
Perform Visual Inspection
The next thing you do is a visual inspection of the fuel system. This will help you determine where the problem is and how to fix it. Make sure that there are no damages to the wiring and harness. Also, inspect for any leaks in the fuel lines, especially near the connectors. If you find any leaks, fix them immediately, which will worsen the problem.
Check for Fuel Pressure
If the code persists, you will need to test the sensor against a mechanical gauge. To do this:
- Turn off the ignition, then attach the fuel pressure gauge.
- Connect the scan tool and monitor the fuel pressure on it.
- Turn the key ON and compare the pressure indicated on the gauge with the scan tool's display.
- The scan tool and gauge should show the same psi amount of pressure. It should be (5) five psi.
- If the results are different, the fuel pressure sensor is faulty and must be replaced.
Inspect the Fuel Rail Pressure Sensor
Another critical component to check is the fuel rail pressure sensor. Locate the sensor and check if it's damaged or not. If it is damaged, you will need to replace it right away. If it's not, you can try cleaning it with a cloth.
Inspect the sensor if it looks corroded or burnt. You can use an electrical contact cleaner to clean the terminals. If the electrical cleaner is not available, you can use 91% rubbing alcohol and a light plastic bristle brush to clean them. After that, let them dry completely, then apply dielectric silicone compound to the contact points.
How to Fix Code P0191?
Once you have finished checking the components and any repair has been made, start the engine and see if the code returns. If it does, you will need to take further diagnosis and repairs. This time you might need to replace the fuel rail pressure sensor.
Step-by-Step Guide to Replacing the Fuel Rail Pressure Sensor
If cleaning the fuel rail pressure sensor did nothing to fix the issue, replacing it might fix the issue. Here's how to do it:
- Park your car on a flat surface. Make sure that the brake park is active.
- Disconnect the negative battery cable.
- Remove the engine cover and brackets that may be in the way of the fuel rail sensor.
- Locate the fuel rail pressure sensor. It will be attached to the fuel rail.
- Remove the electrical connector from the sensor.
- Remove the old sensor using a ratchet and socket.
- Install the new sensor and hand-tighten it with the ratchet and socket.
- Reconnect the electrical connector to the new sensor.
- Reinstall the engine cover and brackets.
- Reconnect the negative battery cable.
If replacing the fuel rail pressure sensor didn't fix the issue, then there's a high chance that the PCM is faulty and needs to be replaced. If you are unsure how to perform it, you may visit our guide to fixing the PCM.
Common Mistakes When Diagnosing the Code P0191
Diagnosing a car issue is undoubtedly not a simple process, and even the best mechanic can sometimes make a mistake. So, do you. However, you can prevent making the same mistakes by avoiding these:
- Checking the wrong sensor (always check your manuals as sensor location may vary depending on your car's make and model)
- Not checking the wiring harness
- Replacing the fuel rail sensor without trying to clean it
- Replacing the PCM when the real cause is failed fuel rail sensor.
- Not checking for other codes associated with the P0191 code.
P0191 Code FAQs
1. Is the code P0191 serious?
Yes, this error code may be considered severe as it can cause engine issues, such as hesitation and acceleration.
2. Can I drive with this error code?
Yes, you can drive, but it is not safe! Would you still drive knowing that it's not safe? Now, ask yourself should I drive? The answer depends on you!
3. What can I do to prevent this trouble code from coming back?
There is no assurance that this code will not return; however, you can do a few things to help prevent it. These include:
- Checking the fuel pressure and ensuring it is consistent
- Inspecting your fuel lines for leaks or damage
- Ensuring that all of your vacuum lines are correctly connected and in good condition
- Checking your fuel rail pressure regularly
4. Do I need special tools to diagnose and fix this code?
To accurately diagnose this code, you will need an OBD scanner and basic automobile tools such as a voltmeter, wrench, screwdriver, and ratchet.
5. What will happen if I don't address this issue?
If you do not address this trouble code, it can lead to drivability issues such as hard start, misfire, and poor fuel economy.
There you have it. If your car is displaying the P0191 code, don't panic, but do take action and fix the problem as soon as possible. Remember, this code is serious, and it could damage your engine if left unchecked. We hope our guide was helpful and that you're now equipped to tackle this issue head-on.
How'd your diagnosing experience go? Let us know in the comments below!