P0401, Beating head against wall. | Ford Explorer Forums - Serious Explorations

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P0401, Beating head against wall.


New Member
April 28, 2020
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City, State
Villa Ridge
Year, Model & Trim Level
2004 Explorer V8 XLT
Hello all,

04 Explorer V8 XLT. When I bought the vehicle it had P0401 code. I was told not to park it nose down on an incline as it would misfire for a while, I thought that was odd but the price was right.

Get it home and start looking into it discovered water pump was bad. Changed water pump and fan clutch. Ran it in driveway to build pressure and check for leaks. Found water coming down at a fast rate in the bell housing area. Again found that odd but figured the intake gasket was bad. Tear the intake off only to find it was cracked in several places around the water jackets.

Well the P0401 was going to wait until the intake was replaced. I patched up the cracks and drove for 4 months like it was.

Changed the intake out, egr, and egr tube (as I broke the original), egr tube fitting, right rear wheel knuckle, right front strut, attempted to change the left front strut however that lower bolt won the first round, 8 injectors, 8 spark plugs, radiator (some engineer needs shot over that design), and a few other odds and ins.

I did reset the PCM by grounding the negative cable to the positive. After the first 40 miles the MIL lite up again. With the original code P0401.

Tried doing KOEO test and it would not complete, figure due to the code. Same thing with KOER, only it gives a reason for not completing (P1400 I believe). When it was going through the test I can hear it open the egr because it will start stumbling.

Hooked up a multimeter to check voltages at the DPFE. Readings starting from top left; 13 v, 5 v, 5 v. Bottom row left to right; 13 v, 0.2 v, 0.4 v. The 0.2 and 0.4 volts increased with throttle input.

Now the EGR was from R.A. not a premium version either. The vacuum lines going to the valve are in good shape.

Is this just a case of a bad part, or is there something that I'm missing?

Unfortunately I don't have a bidirectional scanner, I can see freeze frame data though.

Any help would be greatly appreciated.
Thank you,


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Made a series of gaskets with variable inlet hole sizes from quarter inch up to 5/8 inch as a way to induce a change in pressure. I need to just get this to pass a darn emission test. Hopefully one of the sizes tricks it to thinking it's right.


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The info techguru gave is good. Back in the olden days when I was doing auto repairs and egr valve started showing up those buggers would carbon up in the port wicked bad and pretty much block off flow.

Had this code recently on my 02 4.6. Removed the intake to check for carbon build up and was surprised at how clean it was about after about 160k miles. Checked the operation of the egr at this point and operated fine. Ordered and replaced the dpfe sensor and end of problems.

Just as an update I replaced the replacement EGR with one purchased at a local parts store. This appears to be the fix. A few days driving will tell for sure. With scanner watching live data shows EGR operation.

Guess I will have either go through the return hassle of Rock Auto or just eat that cost.