What were the actual code numbers? The reason I ask this is I have been doing this for many years and I see people who have been doing this for twice as long as I have, but will blindly, and incorrectly, diagnose something because they are definitely not technicians, nor mechanics, but rather, just parts changers. Had a self-professed Mazda "technician" of 26 years tell me that a DTC P0420 on a 99 Miata was "an oxygen sensor", didn't state upstream or downstream or could even explain why it only tripped a P0420 (Which is Catalyst Efficiency Below Threshold) and not the 65 other codes specifically tied to oxygen sensors. His answer to that was how long he had been working on Mazdas. I explained to him the only condition in which that code is set, is when the downstream oxygen sensor is switching from lean to rich in the same pattern as the upstream oxygen sensor. Once the catalytic converter reaches operating temperature, no matter the engine's RPM, what comes out of the catalytic converter, and is read by the downstream oxygen sensor, is a constant reading, therefore the only way the downstream sensor will switch is when the catalyst within the converter has broken apart and failed. He told me I didn't know what I was talking about.
And oh my, I got a good bit off topic there didn't I. So.. number one, get the actual DTCs, not some random "diagnosis" from a "mechanic".
Now concerning the DPFE sensor, which stands for Differential Pressure Feedback EGR sensor. It is a rectangular-shaped box not longer than 3" that has an electrical connector and two vacuum lines running into it. These vacuum lines go to the metal line that runs between the EGR valve and the exhaust manifold. Two things to note with this, depending on your year, a factory DPFE sensor will have the vacuum lines back-to-back, whereas an aftermarket (Or later production factory unit) DPFE sensor will have the vacuum lines side-to-side. Ford made this design change after numerous sensors melted themselves. Second thing to note, check your sensor with a multimeter, much like an oxygen sensor, the voltage on the reference wire will change under different operating conditions (Idle vs WOT). When the DPFE fails, the voltage usually sticks at one end or the other which generates the DTC EGR Flow Insufficient or EGR Flow Excessive, and in some cases generates both DTCs. Another less scientific way to check the DPFE sensor is to pull of the vacuum hoses and if you notice any brownish or greyish carbon build-up in the hoses, the sensor is sure to have failed.
I have known people to go through several DPFE sensors in the course of vehicle ownership, in both of my Vulcan-powered beasts, I have only replaced them once in each. On both vehicles I removed the EGR sampling tube and cleaned it thoroughly, I also cleaned or replaced the vacuum hoses. Since carbon stuffing up in these sensors kills them, it makes no sense to replace a sensor then shove the carbon-filled vacuum hoses onto it's nipples.
On the MAF sensor, again, impossible to tell the severity or accuracy of the "diagnosis" without the DTC at least. However if there was an actual problem with the MAF sensor, you would have severe driveability issues.
