EGR Valve

Did you use a factory valve? Are the EGR passages totally clean of carbon. If so, then you need a scanner to zero the new EGR valve. if you did not use the proper Delco/Delphi valve and really clean the passages, the light will not go off. I have seen people get after market valves for GM Digital EGR systems and they never can get the light off. A good data scan of the input values is also a good thing to consider in order to make sure that the wiring is ok. Best of Luck