OBD2 Codes List
Looking for a free OBD2 codes list? Find out what is wrong with your vehicle and how to fix it with our list of OBDII trouble codes.
OBD 2 codes can be very confusing. Many people think 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 OBD2 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 have listed the common causes for each type of trouble code below… including additional details on what triggers it in the first place.
OBDII Codes 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 OBD2 code, and it could be even just a false reading.
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.
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.
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.
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.
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.
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.
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. Find out what would trigger this OBD2 code.
P0442 Evaporative Emission Control System Leak Detected
Small to Medium Leak – This is an OBD2 code that will set when you have a leak in the evap system. Sometimes you can find this leak yourself.
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. Find out what are the most common causes of this OBDII code right here.
To troubleshoot, repair and maintain your vehicle, you’ll need diagnostic and repair information that is specific to your car or truck. For this I personally use and recommend ALLDATAdiy. With full manuals for over 30,000 vehicles online, you will find an exact match for your vehicle’s year, make and model.
Besides being cheaper than a factory manual, they also offer step by step repair instructions and detailed diagrams beyond what is found in most printed manuals. Click here for a sample of their diagnostic and repair information.