2002 P0401 code and DPFE
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Junior Member
Joined: Dec 2005
Posts: 6
Likes: 0
From: Arizona
2002 P0401 code and DPFE
Hello all,
My specs: 2002 F-150 superduty with a 4.6 V8
I getting a P0401 code from my check engine light. I bought a new DPFE sensor from the Ford dealership and installed. I had the same problem 4 yrs ago and a new DPFE fixed the problem. I cleared the CEL and after about 10 miles it came back with P0401 again.
I then removed the EGR valve and the steel tube to the exhaust manifold and both were clear of any carbon build up. While I had the EGR off I applied vacuum to the valve and watched the diaphram. It opened and stayed open until I released the vacuum. After I reinstalled the EGR I applied vacuum to it while the engine was running and the engine rpm bogged down. When I released the vacuum the engine rpm returned to normal.
I replaced the EGR vacuum solenoid and cleared the fault again but once again the CEL came back after about 10 miles.
On the 3 wires going to the DPFE here are my voltage readings with key on engine off:
VREF is constant at 5VDC
Signal Return is constant at 0VDC
DPFE Signal is 1.1 VDC with key on eng off, 1.25VDC with engine running and vacuum applied to EGR valve ( engine bogging down )
Am I correct on the DPFE voltage or can anyone help me with any ideas?
Thank you!!
My specs: 2002 F-150 superduty with a 4.6 V8
I getting a P0401 code from my check engine light. I bought a new DPFE sensor from the Ford dealership and installed. I had the same problem 4 yrs ago and a new DPFE fixed the problem. I cleared the CEL and after about 10 miles it came back with P0401 again.
I then removed the EGR valve and the steel tube to the exhaust manifold and both were clear of any carbon build up. While I had the EGR off I applied vacuum to the valve and watched the diaphram. It opened and stayed open until I released the vacuum. After I reinstalled the EGR I applied vacuum to it while the engine was running and the engine rpm bogged down. When I released the vacuum the engine rpm returned to normal.
I replaced the EGR vacuum solenoid and cleared the fault again but once again the CEL came back after about 10 miles.
On the 3 wires going to the DPFE here are my voltage readings with key on engine off:
VREF is constant at 5VDC
Signal Return is constant at 0VDC
DPFE Signal is 1.1 VDC with key on eng off, 1.25VDC with engine running and vacuum applied to EGR valve ( engine bogging down )
Am I correct on the DPFE voltage or can anyone help me with any ideas?
Thank you!!
Last edited by AZallen; Jun 2, 2011 at 05:46 PM.
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
Seems you covered all the common areas.
Look at the DPFE hoses for cracks or being reversed.
Check the vacuum hose from the intake to the EVR.
Next if you have a good scanner, do a KOER to see is code 1408 results. If yes there is still a hard fault.
It could be wire harrness/plug related or back toward the PCM.
The 401 test is a 'controlled' opening of the EGR to meaure flow pressure across an orfice in the metal tube by the DPFE that reports the result back to the PCM.
The test is very tight in tolerence and is why this code failure comes up so often.
Testing voltages on the DPFE is not to productive because you are not measuring it's ability to output under a pressure changes from the ports. It's always possible the new DPFE is not good.
Keep at it.
Good luck.
Look at the DPFE hoses for cracks or being reversed.
Check the vacuum hose from the intake to the EVR.
Next if you have a good scanner, do a KOER to see is code 1408 results. If yes there is still a hard fault.
It could be wire harrness/plug related or back toward the PCM.
The 401 test is a 'controlled' opening of the EGR to meaure flow pressure across an orfice in the metal tube by the DPFE that reports the result back to the PCM.
The test is very tight in tolerence and is why this code failure comes up so often.
Testing voltages on the DPFE is not to productive because you are not measuring it's ability to output under a pressure changes from the ports. It's always possible the new DPFE is not good.
Keep at it.
Good luck.
Technical Article Contributor
Joined: Oct 2005
Posts: 25,641
Likes: 19
From: MI
I don't think you need this right now, but your may at some point. I made a little reference sheet and video w/voltages for a couple guys awhile back. A proper functioning dpfe/EGR =
https://www.f150online.com/forums/3805252-post47.html
https://www.f150online.com/forums/3805252-post47.html
Thread Starter
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Junior Member
Joined: Dec 2005
Posts: 6
Likes: 0
From: Arizona
Thanks guys! I have seen a lot of posts about the plenum being plugged and not allowing enough vacuum to be pulled through the EGR. I think since my truck has 135,000 miles on it the ports probably need cleaned. At least I'll eliminate that cause. I think I saw a step by step procedure posted.
Thanks again!!!
Thanks again!!!
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
Yes that will do it.
The exhaust is under some pressure and the intake under vaccum.
If there is no flow through the orface in the metal tube the DPFE cannot measure it and reports it as a failure.
Good luck.
The exhaust is under some pressure and the intake under vaccum.
If there is no flow through the orface in the metal tube the DPFE cannot measure it and reports it as a failure.
Good luck.
Thread Starter
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Junior Member
Joined: Dec 2005
Posts: 6
Likes: 0
From: Arizona
Me and a buddy just finished pulling the plenum off my truck. Just as you said, One port was blocked solid and one was almost blocked. We cleaned all the carbon out and reinstalled. Pretty easy job. Now when I apply vacuum to the EGR the motor really drops rpms. I cleared the CEL and hopefully it won't return. Thanks again for your knowledge!!!