well my inspection and reg is due and i cant get either cause of a p0405 egr problem. a couple of ??

I had a 04501 code in the past and see other codes like 0401,0403,0405 are they all the same ? why diffrent #s ?

i used to clean out the port with carb cleaner but its not working anymore and was looking at the egr snake on a post here. does anyone know the size of the hole for the egr port i dont want to over drill a hole and cause any bigger porblem? is there anything better to clean it with? i think it said the snake was 3/16 and how long is that tube? help quick as my reg expired 2 weeks ago