Ford EGR System - Know the system and you can fix it

If you know how something works... you can fix it. No matter what system you deal with on a car or truck, it can be fixed if you have the right knowledge and information. Some technicians do not have the luxury of factory service manuals for every vehicle that rolls into the shop. A computer system with technical information like AllData or Mitchell on Demand may not be available either. In these cases it is even more important for the technician to understand the effected system. In other cases, if a trouble tree is available, it might not explain what is being checked in each step and may confuse the technician even further. Besides, could technical information ever contain typographical errors?
My point is simple: knowledge is a valuable tool. Understanding whatever system you are trying to diagnose makes all of the difference in the world. Some printed technical materials you cannot live without, while others seem to make no sense at all. As a result we need to step back and use all of our tools, including available literature and our minds, to solve problems. The few moments it takes to review our options can save valuable time and effort. These same few moments also present multiple plans of attack. These plans are fabricated from literature, knowledge, and experience.
To illustrate my point I have chosen a Ford Exhaust Gas Recirculation system. Fords usually set PFE (Pressure Feedback Egr), DPFE (Delta Pressure Feedback Egr), or EVP (Egr Valve Position) sensor codes when a problem is detected in the EGR system. Although these sensors are common failures on these vehicles, you cannot afford to jump to conclusions. The incorrect sensor value could be a result of a malfunctioning mechanical component. Swapping a sensor and sending the car down the road could come back to bite you. So what route should we take to solve these problems?
To answer this question we will be attacking a P0401 on a 2000 Ford Explorer. The first step is to break the system down into it’s three base parts. These three parts remain the same from the early 1980’s to the present. They are as follows: the mechanical system, the control system, and the feedback system. down Because Ford EGR systems have been very similar for more than two decades this procedure works on almost all Ford products.

Source