Ford Repair: Check engine light/ EGR, vacuum lines, vacuum line

Question
Hey, I have a 99 Ford F150 the check engine light is on and the it coded i the EGR needed replaced. But i have already replaced the EGR and even the mechanic can't figure out why the light will not go out and why the truck still codes that the same way. The diagnostics is not working for us if we keep getting the same code problem. The mechanic tired resetting the engine light it worked for minutes. What problem could me and the mechanic be missing?

Answer
it would be helpful to know what engine is in this vehicle but here are a few possibilities. if this is a v6 and you are receiving a p0401. replace the d.p.f.e. sensor. if this is a v8, and receiving this code replaced the d.p.f.e. sensor, also inspect for holes or burn marks through the hoses that go to this sensor. if they are o.k. follow the vacuum line back from the egr, it will lead to what is called a e.v.r. solenoid, there you will find two vacuum lines. one of them has a crack in it !!