How to Use a Code Reader

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What do you do when your check engine light comes on? What does it mean? It means that your vehicle's engine management system has detected a problem and set a diagnostic trouble code. Before 1996, manufacturers used different data link connectors to communicate with the vehicles. This is referred to as OBD I (On Board Diagnostics I). OBD II covers all passenger cars and light trucks built for sale in the U.S. 1996-present. Any vehicle with a GVW (Gross Vehicle Weight) up to 8,500 has to be OBDII Compliant (California GVW 1400). Any vehicle over the GVW of 8,500 (i.e. Medium/Heavy Duty trucks) may not be compliant - this information can be found on a sticker located on the driver's doorframe.

It is easy to read trouble codes from an OBD II vehicle with the help of an affordable tool called a code reader. Many different tools and brands are available, from simple code readers which just give you the code, up to professional scanners which run many diagnostic tests. Some of the simplest code readers we offer are the Actron CP9125, Actron CP9550, AutoXray Code Scout 700 and the Equus 3030 Code Reader. A great book for beginners is How to Use Automotive Diagnostic Scanners, item number 0760328002.

Once you have a code reader or code scanner tool, you will locate the diagnostic link connect (DLC) in your car or truck. It is usually under the driver's side dash, and with all OBDII vehicles, it will be within two feet of the steering wheel. Insert the code reader's plug into the DLC outlet. Turn the ignition key to the "on" position. You will need to read the user's manual that came with your code reader or code scanner to fully understand the functions. In general, there may be a "read codes" button and arrow buttons to scroll through the codes. Some tools will just tell you the code, others will also state the code definition. Your code reader or code scanner will also allow you to erase the trouble code. But please keep in mind that you will need to repair the problem which triggered the code in the first place.

Now that you have your trouble codes, many references are available to help you find the definition and possible causes of your problem. You can use a Haynes or Chilton repair manual or a trouble code book such as 1998 - 2011 AutoData Trouble Codes with Probable Causes Book Bundle - Domestic & Import, item number 11340-11350. You can try to troubleshoot & repair the problem yourself, or take your vehicle to a professional mechanic. Even if you end up taking it to the pros, at least you already have a good idea of what is wrong with your car.

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