When The "Check-Engine" Light Comes On, What Does It Mean?

When the Check-Engine light comes on in your car, it means that the computer which controls your engine has detected some kind of problem in the computer control system and has stored a "Diagnostic Trouble Code" (DTC) which identifies the fault it has detected.

See Our => Showcase Of Automotive Diagnostic Trouble Code Readers And Scan Tools <=

Also see => Computer Code Readers and Scanners at J.C. Whitney

You cannot get the OBD II codes without using a code reader or a scan tool (scanner)!

AND THEN WHAT?

ALLDATA DIY - Detailed Information Online For Your Particular Car,
including step-by-step directions for solving each Diagnostic Trouble Code (DTC).

IF THE CHECK-ENGINE LIGHT COMES ON, IT MEANS TROUBLE CODE(S) ARE STORED!

IT IS 100% NECESSARY for you to be able to obtain the Diagnostic Trouble Codes (DTC's) stored for any computer-controlled engine you are trying to work on. Almost every car sold in the USA since the late 1980's has a computer-controlled engine. And, by law, every car sold in the USA since 1996 must have an OBD II ("On-Board Diagnostics 2") system of reporting these codes. If you cannot obtain these codes, you cannot possibly do complete and efficient work on engine performance. Even if you don't do the work yourself, you still need these codes to understand what is going on with your car.

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NOTE REGARDING CODE READERS: The CAN Protocol (Computer Area Network) is used in some cars starting in 2003, and it will be mandatory in all USA cars by 2008. Many code readers do not support the CAN Protocol, so if you want to be able to read the CAN-protocol codes, be sure that the code reader you choose is "CAN capable" or "CAN enabled." To be sure, you should carefully read the product description of the exact code reader you are considering, to see that this exact one is CAN-enabled. Some older-version Code Readers may not be CAN-enabled, even though they have the same Model Number as newer versions which are CAN enabled. Buyer beware! Be sure to read the Product Descriptions for the exact ones you are considering from each different seller.

Automotive Diagnostic Trouble Codes (DTC's)

See Our => Showcase Of Automotive Diagnostic Trouble Code Readers And Scan Tools <=

Also see =>

You cannot get the OBD II codes without using a code reader or a scan tool (scanner)!

And after you get the codes, what do you do with them? See ALLDATA for complete information!

ALLDATA DIY - Detailed Information For Your Particular Car, including exact definitions
and step-by-step directions for dealing with each Diagnostic Trouble Code (DTC).

OBTAIN EARLIER CODES WITHOUT A CODE READER

Most of the pre-OBD II cars (pre-1996) do have a way that you can obtain the codes without having a code reader. There are many different systems for the different kinds of cars, but they are mostly all covered in this book, " The Haynes Computer Codes and Electronic Engine Management Systems Manual."

This book also provides an excellent basis for understanding how automotive engine computers and computer codes work.

After You Get The Codes, Then What Do You Do?

The ALLDATA DIY online service will give you the exact definitions for each code for your particular car, and then will tell you what to do about each code.

But then, once you have the codes and their definitions, what do you do with them? How do you use them to solve the problems with your car? In my opinion, the very best thing to do is to use the online, interactive DTC information, specifically edited for your particular car, at AllData DIY (Do-It-Yourself), the premier online source for automobile repair information. AllData will tell you step-by-step what to do with each particular code you have gotten.

ALLDATA DIY - Detailed Information For Your Particular Car, including exact definitions
and step-by-step directions for dealing with each Diagnostic Trouble Code (DTC).

Also see our Automotive Glossary entry for Code Readers And Scan Tools

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