P0400 Nissan -

Question

how to test solenoid switch

Answer 1

You should try to clean the EGR and its piping first.

here is how to diagnose the problem.

 

Comments

I have replaced the EGR cleaned the main tube, replaced the temp sensor, the solenoid sensor, and just about every other part connected to the EGR.  it still throws a 400 code, so we are thinking the solenoid sensor is bad because I got it at a junk yard.  How can I tell if it is?