Engine Light always on, help

[mark241307]

Ok, my 2000 frontier 4x4 3.3 manual, is throwing code p1400 for EGR witch looks to be fine. Also I am getting p0325 for knock sensor. At first I was going to replace the O2 sensors but saw the codes and thought differently. Is there something I can clean or check. Do these codes mean something that I am over looking. I am gonna disconnect the battery and wait to see if the codes clear. I think they will come back though and I wanna get the immitions right so I can get the stickers. I know the exhaust will need some work eventually, but I want to get rid of the codes 1st. Can anyone help me with a list of things to test. Maybe in order from easiest to hardest. Is there a way to check the O2 sencors? I really need to get this car legal 2day or 2morrow and they wont inspect it with the check engine like on~ Thanks for reading~

[JaredGuess]

Is the car detonating? Have you listened? Used a good conductor? Adjusted the timing and reset the code to see if it pops again?