I'm trying to figure out exactly what my issue is with a P0400 code. I also have a p0325 code which is a knock sensor. (understand that one). I have replaced the egr valve and cleaned the egr tube (which was clogged on the top port) but today after driving for a few miles the light came on again. I spoke with someone at the auto parts store and he said to check the breather tube at the gas tank filler hose? Have any of you had this problem and what did you do to correct it? Also what other things can I check. I don't want to keep throwing money at this but time is running out on my inspection.
Any constructive comments would be appreciated.

Thanks

 

Check your egr solenoid switch. It's small little green box that controls the function of the egr system.

 

Someone said that you could check for continuity on that switch which I did and it does show continuity. Is that a good check or is there something else I can do?

 

Checking continuity is only testing half of the switch, the electrical side. The device has 3 vacuum hoses on in and it will switch one of the lines between the other two. This switching part could be bad and a continuity test would never show it.

In the service manual, it shows how to test the switching section. Click on the link below and follow the directions on page 261.

The link is to a 1998 manual. You didn't say what year your car is, but you got lucky this time as this is the same for all the years.

http://boredmder.com/FSMs/Nissan/Maxima/1998/EC.pdf

 

p0400 egr valve flow A