My check engine light just came on today. Is there an easy way to check the codes on these things and is this something that I need to let the truck sit until it is checked or can it be ignored for a day or two. it is a 99 3/4ton 4wd with a k & n breather kit and Comp box on it.

 

If you hold the trip/odometer button in while turning the key to the 'on' position, the computer will go into a self check mode.The gauges will all max out, one by one in this mode. When it is done in this mode, turn the key off. Then, turn the key on-off 3 times, ending in the on positon to retreive the codes. Below is a link that takes you right to the OBDII list of codes. <br><br>http://www.obdii.com/codes.html

 

I don't think the 99 will display the codes. If not, go to Autozone and they will read them for you free of charge.