96 GMC 1500 5.7 this problem has been reoccurring. Missfire on the 4 cylinder. It comes and goes. The check engine light would come on then off when I dropped the trailer or when pulling a hill. Loss of power and obvious engine smoothness. Had several mechanics put their computer on it and the computer wouldn't store codes so.. it did relay that it was the 4th cylinder. Now it runs horrible and gobbled up a tank of fuel in 150 mls. Now its consistent ...runs like ****!

SOURCE: 1996 GMC Sierra 1500 truck fuel problem

Have you check the injector relay or maybe a fuse for injectors.

SOURCE: check engine light on 2005 gmc youkon

engine lght is on - lack of power

SOURCE: my 2003 gmc yukon stalls

Had similar problem with my 2001 pontiac grand prix. replace engine coolant temperature sensor. Vehicle may start , but run very poorly, blowing black smoke, running very rough and misfiring. Cost $15 autozone.

SOURCE: 2002 GMC Yukon, erratic idle(hi-low) when cold. 125K miles.

i now for a fact that it is the egr valve . carbon balls in side you have to take it of and clean them out

SOURCE: My engine light has come on in my 2004 GMC crew

If the light was flashing when it came on, then it means your engine is misfiring.

A solid light can mean anything from a loose/faulty gas cap to a transmission issue.

This light comes on when the computer detects a fault of some sort in its diagnostic tests. If it keeps detecting this issue, the light will remain on. If the light turns off, then it has detected that the issue may no longer be present.

In order to find out what the exact reason was for your light, You need to have your car computer scanned to retrieve the code that the computer would have stored when the light triggered. Most garages will do this free of charge. The code will tell you what may have caused the light to initially turn on. Until you get this code, it's impossible to determine what parts need to be checked or replaced.