My 2002 SCREW with 4.6 engine has a P0406 code(EGR flow sensor A circuit high input). I replaced the stock air filter with the K&N filter. I havent been able to find much info for this code any help would be greatly appreciated.thanks

 

This code involves the DPFE sensor connection hoses.
After start up, and in acceleration, a test is made of these hoses, connections and hardware.
This is done when the PCM looks at the output from the DPFE with exhaust pressure against both sides equally.
Since at 'no EGR flow' the pressure at both hoses should be the same or amount to a zero sum out of both hose ports.
If this is not the case, the PCM concludes there is a problem with one of the hose conections or pipe hardware.
Check DPFE hoses all over well and be sure the hoses are on snug, pipes are not cracked in any way.
It could also be the result of a plugged internal calibrated orfice in the pipe between the two small hose connections.
This orfice is the basis of the measurements the DPFE makes for indicating the relitive inferred condition of the whole EGR system.

 

like bluegrass stated.....ill say it with out the engineering talk... check your vaccum lines make sure you dont have a bad line or it has a hole.. double check..