My check engine light has been on for a couple of days & i have this code P0401 Exhaust Gas Recirculation (EGR) Flow Insufficient Detected . I go out today & start the truck & the light does not come on. I thought the only way for the light to go out was to reset the ECM. What is going on with my truck.

 

If this is like most Fords and what my old Ranger went through with an EGR Insufficient Flow code...your DPFE sensor is bad or the hoses leading into that sensor are crumbling away...

In my Ranger's case, the light was not constantly on either.

But, this is the interweb and you need further diagnosis than what any of us can offer...

 

When the dpfe went out in my van that happened it woulld go out for awhile then come back on. eventually it stayed on all the time. I got my dpfe from ford for about $100

 

You may have a marginal DPFE.
Here is some background on how the monitor works.
The 401 test must fail two times in a row to be judged a failure.
So your lamp went out when the 401 test passed 2 attempts at testing by the PCM. That is normal self clearing.
What sometimes can cause this is, in freezing temps., moisture in the exhaust can freeze and block the little test orfice or the DPFE so the DPFE can't get the reading it needs to see, within limits. That is why the two test sequence is applied.
Usually motor heat clears this condition but if the motor is not run long enough, it can happen. In the direction of the DPFE, the moisture can't get out and lays there, causing corrosion etc.
I would test the EGR path from the header, thru the orifice and the EGR port for restriction. When all clear and you still see the code come and go, then it's time to replace the DPFE for internal corrosion or blockage.
I would do the whole check to be sure you cover all possibilities.
With the DPFE hoses removed, you should be able to feel the exhaust pulses coming out of both stand pipes, indicatiing the test restriction orfice is clear.
Put a small amount of vacuum on the EGR where the hose is attached, opening the EGR just enough to see if the idling motor gets rough running. If yes, the EGR works and the port is open.
This leaves the DPFE suspect.

 

Thanks for the replys. I've done all of those tests. I ordered the DPFE sensor & was waiting for it to come in when the light went out & i thought that was odd.