Ford: computer codes for egr valve, congestion problem, diafram

Question
Hello
I have a 97 4 liter 2wd ranger and the engine light came on and I had the code read and it was saying PO40 for EGR system fail what could this be Thanks
Dave

Answer
EGR system failure means the diafram in the valve is
not moving properlly. A congestion problem may be
the culprit. A high or low voltage range problem at the
EGR valve may mean another sensor is having an effect on the EGR system. Check for exhaust congestion in the EGR
system.