I have a 2003 2500HD with the LB7. I just replaced my vacuum pump due to failure. After the pump was replaced, and truck driven a little, the SES light came on. It came up with the P0404 code. I know it has something to do with the EGR but cant figure out how to diagnose the problem. I have read that it might not be the EGR itself.

The truck seems to run fine, no idle or performance issues. After the code was reset, less than 20 miles later the SES light came back, so did the P0404 code.

Any thoughts????