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Common Powertrain OBD II Codes & How to Fix Them – Part 1

Technical  ·  August 24, 2021

Common Powertrain OBD II Codes & How to Fix Them – Part 1

Onboard diagnostics make it much easier to pinpoint problems that might happen in our car. However, understanding the meaning of diagnostic trouble codes does take some work. This article will explore some of the most common OBD II codes related to powertrain faults.

OBD II codes starting with P correspond to the car's powertrain. Some of the most common ones suggest a faulty oxygen sensor, misfiring engine cylinders, problematic evaporative system, and fault catalytic converter. You'll find that several error codes point to similar problems. That's because they overlap, or each code represents the same problem happening at a different part.

Let’s take a closer look at some of the basics you’ll want to know about OBD II fault codes related to the powertrain.

What Do ‘P’ Diagnostic Trouble Codes Mean?

OBD diagnostic trouble codes starting with the alphabet 'P' point to a problem in the vehicle's powertrain.

Remember: Diagnostic trouble codes consist of 5 characters. The first alphabet of that diagnostic trouble code corresponds to the specific subsystem or group of codes related to the problem. 

Besides ‘P’ for powertrain problems, the other codes are:

Common Powertrain OBD2 Codes & How to Fix Them

This section will explore some of the most common powertrain trouble codes, i.e., the ones beginning with the letter P. It's essential to remember that this is not an extensive list. Instead, we'll be highlighting the ones that you’re most likely to experience.

As you’ll see from the list below, several different OBD2 codes can point to the same problem. There are generally two reasons for this:

Now, let’s look at some of the most common powertrain OBD2 trouble codes, what they mean, and what you can do about them.

OBD2 DTC P0171-P0175

Affected part: Faulty Oxygen sensor. This component senses the air-fuel mixture in the engine to ensure that it’s at the correct level.

What is likely happening: If you see any of these OBDII codes, the most likely reason is that the oxygen sensor is faulty. When that happens, your car cannot accurately sense the oxygen levels in the air-fuel mixture. As a result, it can’t make the necessary adjustments to ensure maximum fuel efficiency.

Symptoms: As mentioned above, a faulty oxygen sensor will prevent the car from ensuring an efficient air-fuel mixture. That’s why these OBD II trouble codes typically happen alongside a loss in fuel efficiency. As a result, you might notice that your car burns much more gas than usual. In a worst-case scenario, your engine might stall entirely if the air to fuel ratio is entirely off.

How to fix the problem: Fixing this problem will require you to inspect your car’s oxygen sensor visually and with a voltmeter. A faulty oxygen sensor will have visible damage on it, or it will have an electrical fault. If that’s the case, you will have to replace it with a new oxygen sensor.

OBD2 DTC PO300-P0305

Affected part: Engine cylinders that are misfiring. As mentioned before, a series of fault codes could point to the same problem but in different parts. In this case, these codes simultaneously point to a misfiring problem and the cylinders where it is happening.

What is likely happening: Engine misfires are typically caused by problematic spark plugs. The plugs themselves could be worn out or installed incorrectly, or their wiring could be damaged. Although less likely, misfiring could also happen due to carbon tracking or vacuum leaks in the cylinder.

Symptoms: Engine misfires are also accompanied by symptoms like rough idling, hesitation or shaking during acceleration, and more.

How to fix the problem: In most cases, installing new spark plugs correctly will solve the problem. If the issue is caused by a vacuum leak, a mechanic will need to locate the leak and recommend the appropriate repairs.

OBD2 DTC P0411, P0440, P0442, P0446, P0455

Affected part: Evaporative System. This system keeps the entire fuel system sealed, preventing any vapours from leaking into the environment.

What is likely happening: If these codes were to appear, a part of the system is likely exposed and leaking out fuel vapours. In most cases, that could simply mean that the cap on your fuel tank is not closed correctly. 

Symptoms: Some common symptoms related to this problem are smelling gas inside your car, poor gas mileage or engine performance, and difficulty filling up your gas tank completely.

How to fix the problem: First, you should see if closing your fuel tank cap will resolve the issue. If that doesn’t work, then you will need to inspect your fuel system to identify any leaks that might be present.

OBD2 DTC P0420, P0430

Affected part: Catalytic Converter. This component converts harmful emissions into harmless outputs that come out from the exhaust pipes. The oxygen sensors in the catalytic converter help the car measure how well the fuel is being burned through the engine’s combustion process.

What is likely happening: These codes simply mean that the catalytic converter is not working as efficiently as it should, and that the car is producing more harmful emissions than usual. This problem could be caused by several reasons, including engine misfires (which causes fuel not to burn completely) or even an exhaust leak. 

Symptoms: Symptoms related to this problem include the Check Engine light coming on, lack of engine power, the vehicle using more fuel than usual, and you might sense sulphur or rotten egg smell.

How to fix the problem: The first step here would be to troubleshoot and identify the root cause. So, replacing your catalytic converter is not the first choice here. Instead, the exhaust system needs to be inspected closely for any leaks. 

Plus, the voltages of the various oxygen sensors need to be checked to ensure they are working correctly.

To learn more about OBD II DTC codes, stay tuned to the blog at, You can also use our Car Part Finder tool if you need some auto parts for your car. Just fill out this form, and we’ll do the searching for you!  

By Ray Hasbollah

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