i have a 1997 nissan pickup 2.4 liter.the check engine light came on.had code read (p o 402) egr flow.do i need a new egr valve or could something be stop up.egr valve was replace about 50,000 mile ago.
There’s a good chance that you just need to clean up all of the passages. Here is a great article I have bookmarked: http://www.engine-light-help.com/egr-valve.html
This should also be helpful: http://www.obd-codes.com/p0402
I would just check for blockages first and worry about the more complicated testing if that doesn’t turn up anything.