Understanding the Check Engine Light (MIL, CEL, OBD-II, OBD2) (1996 and newer rigs)

[theksmith]

I did a little article on the basics of OBD-II (the system behind that pesky Check Engine Light) and wanted to share it here:
http://www.offroadpassport.com/forum/showthread.php?t=686

Along with proper tools and spare parts; I think knowing how to pull codes on your particular rig and what they mean is essential to being prepared for mechanical problems in remote areas.

The same concepts apply to pre-1996 vehicles with OBD 1, but my writeup is mainly geared towards OBD 2.

I welcome any comments on improving the article, especially if you see any inaccuracies. Thanks!

 

[R_Lefebvre]

Pretty solid. The only thing I'd say is that you state "monitoring and recording data related to nearly every major system in your vehicle," While that may be accurate to the letter of the law, I don't think it's realistic. I've never seen or heard of anybody ever getting a B or C code. I know for sure on a Land Rover, these functions are always squirelled away in another computer somewhere, and inaccessible by a standard OBDII scanner.

The OBDII requires manufacturers to make these codes available via a generic scanner. But they are NOT required to do the same for body and chassis functions, and usually they don't. It's a big hole in the law, which needs to be updated. When the OBDII system was set up, there were no computers running body functions yet. This is a big part of the "right to repair" debate.