i have 2002 f150 4.2 engine.my question is what is the module in the egr system called.i have a p0401 egr flow insufficinet code and already replaced the egr valve for a code for that.i believe the other module is at fault, but not 100% sure.any advice would be helpful.

 

Its called a DPFE sensor. It could be bad or you could have other EGR system problems. You should hook a vacuum pump to the EGR valve and put vacuum on it. If the motor starts to idle bad the EGR ports are good. If the idle doesn't change you have clogged egr ports. You also need to check for vacuum going to the vacuum valve that controls the egr valve.