I'm getting codes P0404 and P0405 (and SES light) from my '98 Chevy S-10 2.2L 4. Both of these codes relate to the egr valve. I replaced the egr valve with another, but I'm getting the same results. Engine runs fine at all speeds. I also tested the "gray wire" supply voltage which is "right up there" (> 5.0 V). Can anyone give me some ideas for fixing this problem?