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What Are The 10 Most Common Trouble Codes?

What Are The 10 Most Common Trouble Codes?

Some of the common trouble codes your car will deal with include:

Auto Repairs Are EXPENSIVE

  • P0300 – Random/Multiple Cylinder Misfire
  • P0301-P0308 – Direct Cylinder Misfire
  • P0420 or P0430 – Catalyst Efficiency Codes
  • P0141 – Oxygen Sensor Code
  • P0446 – EVAP Code
  • 0455 – EVAP Code
  • P0171 or P0174 – Running Lean Code
  • C0221 – Wheel Speed Sensor Code
  • P0401 – Exhaust Gas Recirculation (EGR) Flow Insufficient
  • P0174 – Fuel Trim System Lean Bank 2

Your vehicle relies on a series of codes to tell you about what's going on wrong internally. Then, using a simple tool like the OBDII, you can easily understand what to expect in terms of repair options and repair costs.

There is a long list of potential trouble codes in your vehicle, which makes it a little bit overwhelming tool the average driver to learn about them all. However, learning about the 10 most common trouble codes is doable and will save you a ton of frustration and effort.

This article walks you through the 10 most common trouble codes, along with their potential causes and solutions.

What are P codes?

Before we dive into the details about the common trouble codes that you might experience, it is critical to understand what the P codes in the first place are.

Over the years, our vehicles became more complicated and involved more internal components. Although this might sound that it becomes harder to diagnose the vehicles and determine problems, that's not the case. On the contrary, the more complicated the vehicles are, the easier it got for technicians and mechanics to determine the problems in the cars.

Your vehicle's computer is very complicated, and when there is an internal problem, it will display a check engine light on the dashboard. However, mechanics can't read and scan the internal computer and display what's known as the pea coats using certain tools.

These codes are a combination of the letter P and some numbers. They refer to different categories related to internal vehicle problems. Typically, the first number will be a general problem in the main category while the other numbers refer to it were within this category's subcategories. Although this might not sound very intuitive to you, it will make more sense for you once you look at the common trouble codes.

What are the most common trouble codes?

Learning about some of the common trouble codes helps save you a ton of frustration, money, and effort. Using a very simple tool like the OBDII scanner, you can get an idea and head up about what's going on with your car. Depending on the tool, you might even get recommendations on potential repair costs and potential repair options.

Let's take a closer look at some of the common trouble codes that your car might encounter and what causes them, along with how to repair the issue:

1-    P0300 – Random/Multiple Cylinder Misfire

P0300 is one of the most common codes that your car might encounter. It refers that multiple things are going on in the cylinders, causing misfiring. So it's not only one thing, but it's a combination of multiple culprits.


Typically, when dealing with a P0300 code, you'll see a check engine light illuminating, and you might notice some shaking in the steering system. This code is most likely related to how the air-fuel mixture ignites in the cylinders, which might be affected by a couple of reasons.


One of the first ways to resolve the issue is by inspecting the fuel supply system. Look at the pressure regulator, the fuel pump, and then move on to the EGR valve for any symptoms of leaks.

It's important to note that the P0300 code doesn't appear by itself, and it will be accompanied by other codes that further explain what's going on and help you determine the issue.


When dealing with this code, you should identify the potential culprit and have it repaired or probably replaced in certain instances.

2-    P0301-P0308 – Direct Cylinder Misfire

The second group of codes you might encounter has to do with some misfiring in one cylinder. It indicates that one cylinder is not contributing the right amount of energy it should.

As you might notice, we grouped these codes in one list because it is related. Typically, the P0301 code indicates that there is a misfiring in cylinder number one. On the other hand, the P0302 code indicates a misfiring in cylinder #2 and so on.

Typically, if you're driving a vehicle with a 6-cylinder engine, you'll have this code going up to P0306. On the other hand, if you're driving a vehicle equipped with an 8-cylinder engine, these codes can go up to P0308.


Engine misfiring is a very general problem. However, there are plenty of symptoms that you might encounter along with this code, including strange in your vehicle’s performance and reduction in the fuel economy.


Depending on the faulty cylinder, there might be a variety of different causes. Start by looking at the spark plugs, check the fuel supply, and consider inspecting the intake valve in some instances.


Once you detect the faulty component, you can resolve it to get rid of this trouble code.

3-    P0420 or P0430 – Catalyst Efficiency Codes

Depending on your vehicle’s engine, you might encounter one of those codes: P0420 or P0430. So, for example, if you are driving a 6-cylinder engine, you'll see in a P0420, and you're driving a vehicle with an 8-cylinder engine, you'll see the P0430.

Despite your engine type, both codes refer to problems with the catalytic converter. When the catalytic converter is not partly working properly, your vehicle will emit more harmful gases to the atmosphere than usual.

In general, depending on the severity of the problem, your vehicle might not pass the emission tests if you're dealing with one of those codes.


Aside from this trouble code, your vehicle will smell a weird smell like sulfur, indicating that the harmful gases are not taken care of and might be getting to the atmosphere.


The only cause for triggering this trouble code is a problem with the catalytic converter.


Obviously, to resolve the issue, you'll have to inspect the catalytic converter and see if it's repairable. Otherwise, you'll have to install a new one. If you don't already know, the catalytic converter is one of the most expensive components in your car, and that's why many people dealing with this code end up giving up on their vehicles.

4-    P0141 – Oxygen Sensor Code

The oxygen sensor code is another common cold that you might experience. It indicates that this sensor located downstream of the catalytic converter is not working properly. This sensor is extremely important because it tells your computer that you are catalytic converter is working perfectly and doing its job or not.


With the check engine light, you might experience some rough engine running or probably a reduction in your vehicle's fuel economy.


Typically, you recommended checking the electric connections between the sensor and the surrounding components. Also, look at the heater circuit or the fuses.


Depending on the root of the problem, you can either replace the faulty component or fix any issues in the connections.


5-    P0446 – EVAP Code

The P0446 is another code indicating that your EVAP system is not working properly. In other words, this code is triggered whenever there is trouble in the system that is responsible for collecting any evaporative emissions as your engine burns the air-fuel mixture carrot


You'll notice a check engine light illuminating immediately, but you might also experience some weird fuel odor in difficult situations.


The EVAP system is a little bit complicated, which means it can be a little hard to detect the actual component causing the issue here; therefore, you'll need to perform a detailed diagnostic to confirm the real culprit.


Once the culprit is identified, you need to get it replaced to resolve the problem.

6-    P0455 – EVAP Code

The P0455 is another common code related to the EVAP system, which indicates an internal leak in the system. Typically, the collected vapors from the combustion process should not leak anywhere around your engine compartment, and when this happens, it leads to significant issues.


In general, dealing with the P0455 code will be associated with a check engine light illuminating and a strong fuel smell around the fuel tank.


One of the most common reasons for this trouble code is losing fuel gas caps. However, the problem might be linked to a crack in the system, which makes it challenging to identify the root of the problem.


Start by tightening the fuel cap as a first way to get rid of this code. If it didn't go away, have your mechanic perform a thorough inspection to confirm where the issue is coming from and resolve it.

7-    P0171 or P0174 – Running Lean Code

The P0171 or P0174 codes are related to troubles with your engine's combustion process. Typically, these codes are triggered when your engine is burning more air than fuel or what's referred to as running lean.


When these codes are triggered, you'll deal with engine coughing and a check engine light illuminating along with a reduction in your vehicle's power.


There are many reasons to trigger these codes, including anything that has to do with the air or fuel supply. For instance, if you're dealing with a clogged fuel filter, you'll have this issue. Also, that fuel pressure regulator and it is connected holds might trigger these codes.


To resolve these codes, take a closer look at the fuel system and the air intake valves to confirm what's causing the issue. Once the culprit is confirmed, you can fix it or replace it if needed.


8-    C0221 – Wheel Speed Sensor Code

In some instances, you might deal with a C0221 code, which indicates that the right front wheel speed sensor has an issue. The sensor is extremely critical when it comes to the anti-lock braking system.


When this sensor is not working properly, you might see a lock brake system or a BS system warning light illuminating on the dashboard along with the check engine light.


Typically, this sensor might go bad due to a problem with the connectivity or the speed sensor harness.


Of course, to get rid of the C0221 trouble code, you'll have to either replace or repair the sensor.

9-    P0401 – Exhaust Gas Recirculation (EGR) Flow Insufficient

There are some other list common codes that you might experience, including the P0401 code. This code indicates that the exhaust gas recirculation is not working properly, impacting how the intake manifold opens and lets gases flow.

10- P0174 – Fuel Trim System Lean Bank 2

You also might experience the P0174 less rare trouble code, which refers to a bad fuel trim system in bank 2 of your engine.


Determining car problems is not as complicated as before. Thanks to the P codes that your vehicle shares with you to bring your attention to internal problems. This article walked you through the 10 most common trouble codes your car might experience during its lifetime. It also highlights what causes these troubles and how to resolve the issues.

Depending on the trouble code you're dealing with, sometimes repair costs might be very expensive shared that's when automotive experts recommend selling your car and using the value to purchase a better vehicle that doesn't have such a problem.

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