Ford 4.6 and 5.4L mod motors use a DPFE to measure exhaust pressure accross a restriction in the EGR pipe to tell what the flow conditions are for EGR gas recirculation.
It is a 0 to 5 volt device.
This detects any loss of pressure due to a leak, excessive pressure, plugged EGR port and inop EGR valve circuit.
All logic driven for results.
The PCM routine calls for pulewidth driven signal to the vacuum gate that operates the EGR valve to a known opening and flow rate. The routine then measures for an expected result of a flow test from pressure detection by the DPFE. If out of limits, a DTC code is set and the check engine light comes on.
When the engine is first started, the device is addressed to see if there is excessive flow indicating a cracked/rusted pipe, a hose off etc. A blocked exhaust system can even cause excess pressure and be detected since the EGR is not open at this time.
Device is not very large and is connected with short hoses on the EGR stand pipes located each side of the internal restriction.
Within a combination of routines, hardware configs and expected reaults, an inferred result is registered in a table as either a pass or fail.