OBD 2 Codes List 

OBD 2 codes can be very confusing. Many people thing that if they have a code that says anything about an 02 sensor that they must need to replace the sensor. In fact this is not how the obd (on board diagnostic) system is supposed to work at all. If you have an 02 sensor code that simply means that the computer has found a problem in the oxygen sensing system. It could be bad wiring, a faulty catalytic converter, a vacuum leak, plugged or leaking fuel injector, etc...and the list goes on. Add to that the fact that people usually talk to their family and friends about this problem (most of whom know very little about the codes) and you have a situation where it is nearly impossible to figure out what is causing the codes.

The following pages and links are here to fix that! I've posted links to pages with diagnostic information about the most common obd 2 codes. Some cars or trucks will have one of two things that will commonly fix certain codes, but for most vehicles there are a list of possible problems that need to be checked out. I've listed most of the common problems that cause each code and a little bit about why the code comes up in the first place. If that doesn't help you enough you can go to the bottom of the page where I've included a link to my Facebook page where you can post your question. Let's take a look at the list. Remember, if you don't find your code on the list, just ask me on my Facebook page. 

OBD Codes Article List

• P0171 System too Lean (Bank 1) This code means that there is too much air entering your engine compared to how much fuel is going in. There are several common causes of this code, and it could be even just a false reading. Read more about how to fix it>>>
• P0174 System too Lean(Bank 2) This code is pretty much the same as p0171 it is just that the condition is found on the opposite side of the exhaust system. You'll be take to the same article, but these two codes are interchangeable. Find out more about lean codes>>>
• P0300 Random/Multiple Cylinder Misfire Detected. This code is likely caused by something other than a single spark plug or a single fuel injector. Since it is for multiple cylinders and/or random it is likely something that affects all cylinders. Things like low compression and multiple plugged injectors will cause it. Here are more common causes>>>
• P0301 Cylinder 1 Misfire Detected. This is an article that covers all of the misfire codes. P0301-p0312...p0301 is for a misfire on cylinder 1 and p0302 is for cylinder 2, etc. Read more about all the things that might be causing your vehicle to be giving you this code>>>
• P0340 Camshaft Position Sensor Circuit Malfunction. There are a good number of things that can cause this code. Many people just go replace their CMP (camshaft position sensor). Then they start driving their car or truck just to find that the check engine light comes right back on with the same code. Don't waste your money! Diagnose it first>>>
• P0401 Exhaust Gas Recirculation Flow Insufficient Detected. EGR (exhaust gas re circulation) codes are tricky. This is another one of the common ones where people just go replace their egr valve only to find that it's not the problem. This system is fairly complicated so be sure to know all the possible causes before you start replacing parts. Check it out>>>
• P0420 Catalyst System Efficiency Below Threshold (Bank 1). The catalytic converter is constantly being monitored by the PCM (using the 02 sensors) to be sure that is cleaning the exhaust properly. When it finds that it's not it will set this code. Before spending $500-$1500 replacing the CAT, find out if there are other things that might be causing the problem (there are!>>>)
• P0440 Evaporative Emission Control System Malfunction. EVAP codes are very tricky and tough to diagnose for a DIY'er. There are a few things you can check yourself though. Read about those here>>>
• P0441 Evaporative Emission Control System Incorrect Purge Flow. The EVAP system is supposed to collect excess fuel vapors and store them until they can be burned in the engine. When they don't flow back to the engine like they should this code comes up. Here are a few of the reasons it might be coming up>>>
• P0442 Evaporative Emission Control System Leak Detected (small to Medium leak). This is an obd 2 code that will set when you have a leak in the evap system. Sometimes you can find this leak yourself. Find out how>>>
• P0455 Evaporative Emission Control System Leak Detected (gross leak). You guessed it! This is a huge leak in the EVAP system. A lot of the time this is something that you can find yourself. Here are the most common causes of this code>>>

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