Understanding Check Engine Codes
Modern cars have computers that can tell you when a problem is detected. The current version of these diagnostic codes is OBD-II, or OnBoard Diagnostic version 2. OBD-II was universally introduced in 1996 and all vehicles sold in the United States since that time will use this system for diagnostics. Some 1994 and 1995 model year vehicles also use OBD-II. These codes can help you or your mechanic know where to look for problems.
Sometimes these codes turn on your check engine light. If your check engine light is on there are certainly codes that can be read to explain why. Other times the light isn't turned on. Even if there is no light there may be an error code that can help you determine the cause of a problem.
The ODB-II code is standardized by the Society of Automotive Engineers, SAE. The first three characters, one letter followed by two numbers, are specified by the standard.
The first character of an OBD-II code designates what system the code relates to. "P" indicates a powertrain problem. "B" tells you that you have a body problem while "C" points to the chassis. For other parts of the vehicle or other problems you might get a code starting with "U" for undefined. Not all vehicles have diagnostics for all parts of the vehicle so you may not see all of these on your particular car.
The second character will be a "1" or a "0". This indicates whether the code is a generic code ("0") or a manufacturer specific code ("1").
The third code tells what subsystem is experiencing a problem. The list of subsystems is,
1 = Emission Management (Fuel or Air)
2 = Injector Circuit (Fuel or Air)
3 = Ignition or Misfire
4 = Emission Control
5 = Vehicle Speed & Idle Control
6 = Computer & Output Circuit
7 = Transmission
8 = Transmission
9 = SAE Reserved
0 = SAE Reserved
The final two digits are used to designate specific problems in a subsystem. This allows for one hundred different generic codes for each subsystem. Allowing for manufacturer specific codes gives the potential for another one hundred codes specific to the manufacturer.
To read the codes you need to use an OBD-II code reader. This allows you to "pull" codes and record them to begin troubleshooting. Readers range in cost from around $75 and up. However, if you don't expect to use a reader often you can usually get the codes read for free at most chain auto parts stores.
Once you have the list of codes present on your vehicle you can begin troubleshooting. Sometimes the code tells you directly where the problem is but it's best not to rely on that directly. Many systems on modern cars can affect other systems either directly or indirectly. If you have more than one code you would be advised to enter all of the codes into an Internet search engine. It is likely that someone else has run across the particular combination you have and has already isolated what kind of problem can cause it.
