[FIXED] 2001 Ford F150 P0401 code

Hello, my 2001 F150 5.4L keeps trowing a P0401 code. Before watching your videos and using a guide I replaced the DPFE sensor with a brand new one from motorcraft. The code will come back as soon I drive it. The EGR valve is working properly and has no leaks. The only test that is not normal is the DPFE flow signal test. Using my voltmeter( DPFE plug still attached to DPFE) I connect the red lead to the top wire of the DPFE plug. The voltage at idle is 1.02v when i apply vacuum the engine starts to idle real rough and the highest voltage I read is 1.27v which is not normal, it should be 3v-5v.

With the engine off key on if I unplug the DPFE wring plug and i use the voltmeter I have 5v on the top wire, the middle wire is ground(confirmed by connecting one lead to 12v at battery) and the bottom wire I get 5v(ref). To me it does sound I have a wiring issue with the top wire or maybe a PCM issue. Any suggestions on how to test to see if I have a bad or fault connection on that wire? I don't have a wring schematic to trace the colors. I bought the truck with 157k miles 3 years ago and i never had any issues with this code.

Thank you. Juan.

Have you checked the egr valve and tube for carbon buildup?

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Hi, the egr valve was replaced witha generic brand one last year. The tube from the egr to the exhaust manifold has not been changed. I pulled the tube out and cleaned it with carb cleaner. As far as i can tell there is no obstruction when i blow air thru it but i can't physically see inside of it. I was going to order a dorman replacement tube but the reviews said it is not a direct fit and it needs to be adjusted. I cleared the code yesterday and i drove today all day and the code just came back.

Ok it's worth checking the valve for carbon . As long as your tube is not restricted don't bother replacing it. Also remove the hoses from the dpfe sensor and make sure neither of them are plugged

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I had checked visually the egr valve and there is no carbon build up. The dpfe hoses were replaced with new ones and the code still persists.

Do you have access to scan data? Checking the DPFE voltage PID can help you determine if there's a wiring problem or not. If the voltmeter agrees with the scan data when you're manually opening the EGR, then I wouldn't worry about the wiring or PCM. Also, the fact that you're getting 5V on the signal wire at the DPFE itself tends to suggest that the wiring is good, as that voltage is coming directly from the PCM.

I see that the engine runs rough when the EGR valve is opened with vacuum, good move. Is 1.27V the highest reading you saw when opening the EGR? If possible, try opening the EGR all the way and raising the engine speed. This should show closer to 4V if the passages are clear.

You've inspected the EGR valve and the tube, so the next place I'd suggest checking is the passages inside the intake itself. This is where the EGR gasses cool rapidly, and where you're most likely to get carbon buildup. You may need to remove the throttle body to get everything cleaned out.

Another thing worth doing is manually energizing the EGR vacuum solenoid, as this will check that all is well with the vacuum hoses and solenoid. Not sure if this is the video you watched, but it describes the procedure perfectly.

Tyler wrote: Do you have access to scan data? Checking the DPFE voltage PID can help you determine if there's a wiring problem or not. If the voltmeter agrees with the scan data when you're manually opening the EGR, then I wouldn't worry about the wiring or PCM. Also, the fact that you're getting 5V on the signal wire at the DPFE itself tends to suggest that the wiring is good, as that voltage is coming directly from the PCM.

I see that the engine runs rough when the EGR valve is opened with vacuum, good move. Is 1.27V the highest reading you saw when opening the EGR? If possible, try opening the EGR all the way and raising the engine speed. This should show closer to 4V if the passages are clear.

You've inspected the EGR valve and the tube, so the next place I'd suggest checking is the passages inside the intake itself. This is where the EGR gasses cool rapidly, and where you're most likely to get carbon buildup. You may need to remove the throttle body to get everything cleaned out.

Another thing worth doing is manually energizing the EGR vacuum solenoid, as this will check that all is well with the vacuum hoses and solenoid. Not sure if this is the video you watched, but it describes the procedure perfectly.

I have a scanner but it it doesn't show dpfe voltage. Yes the highest is 1.27v. There is no carbon build up in the throttle body. I removed it before and both holes are clear.

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jayta98 wrote: There is no carbon build up in the throttle body. I removed it before and both holes are clear.

OK, cool. Sure sounds like our exhaust path is clear, then. Any luck with the EVR test?

Going back to the DPFE sensor, you could try taking the front hose off and using a hand vacuum pump, KOEO. The difference in pressure should make the sensor respond with a positive voltage increase. If you can't get the voltage past the 1.27V you observed earlier, then we should dig deeper into the sensor and the wiring.

you said the dpfe hoses were replaced? are the hoses reversed?? also agree with tyler on testing the dpfe sensor with a vacuum pump

Ok, so I followed the video and the engine won't stall when i use my test light on the left wire of the solenoid. I do have a LED test light not sure if it affects the test.( the one that turns green or red depending on polarity). Using my voltmeter and KOEO I have 12v on each wire like the video shows. If unplug the wire plug I have 12v on the right side wire only again like on the video. I plugged the cable back on the solenoid. With KOER I use the test light connected from 12v (battery) to the left wire of the solenoid and nothing happens. If check the voltage with voltmeter with engine running and it reads 12v on each wire. I believe it should be 12v only on the right side wire only. Am I right?

Tyler wrote:

jayta98 wrote: There is no carbon build up in the throttle body. I removed it before and both holes are clear.

OK, cool. Sure sounds like our exhaust path is clear, then. Any luck with the EVR test?

Going back to the DPFE sensor, you could try taking the front hose off and using a hand vacuum pump, KOEO. The difference in pressure should make the sensor respond with a positive voltage increase. If you can't get the voltage past the 1.27V you observed earlier, then we should dig deeper into the sensor and the wiring.

Ok so I followed your test at DPFE sensor. KOEO with vacuum pump connect in the front port of the sensor. Before I apply vacuum the voltage is about 1.2v. As soon as I apply a little vacuum the voltage is 4.92v. So does this mean the sensor is good? Could be an issue with the small port on the pipe? When I pulled it off I remember there was flow thru the egr outlet but i don't remember if the small ports were clear. any other possibles?

I pulled out the EGR tube. All ports are clear from obstructions, the big ones and small ones. So it is not the tube.

jayta98 wrote: Ok so I followed your test at DPFE sensor. KOEO with vacuum pump connect in the front port of the sensor. Before I apply vacuum the voltage is about 1.2v. As soon as I apply a little vacuum the voltage is 4.92v. So does this mean the sensor is good? Could be an issue with the small port on the pipe? When I pulled it off I remember there was flow thru the egr outlet but i don't remember if the small ports were clear. any other possibles?

Yep, I like the results of that sensor test. Also good to know about the tube ports.

I really hate to nag you about this, but are you POSITIVE the intake ports are clear? Because the only other possibility I can think of is that the replacement EGR valve isn't opening far enough to allow full flow into the intake, and I've never heard of that before. I was initially thinking of the vacuum hoses and the EVR, but we're still getting low DPFE voltage when you open the EGR manually.

Tyler wrote:

jayta98 wrote: Ok so I followed your test at DPFE sensor. KOEO with vacuum pump connect in the front port of the sensor. Before I apply vacuum the voltage is about 1.2v. As soon as I apply a little vacuum the voltage is 4.92v. So does this mean the sensor is good? Could be an issue with the small port on the pipe? When I pulled it off I remember there was flow thru the egr outlet but i don't remember if the small ports were clear. any other possibles?

Yep, I like the results of that sensor test. Also good to know about the tube ports.

I really hate to nag you about this, but are you POSITIVE the intake ports are clear? Because the only other possibility I can think of is that the replacement EGR valve isn't opening far enough to allow full flow into the intake, and I've never heard of that before. I was initially thinking of the vacuum hoses and the EVR, but we're still getting low DPFE voltage when you open the EGR manually.

Hmm I will pull the EGR out tomorrow and check everything again. I guess it could be possible the EGR could be getting stuck. I'm still trying to figure out why did the EVR test failed... I followed the video and nothing happened. I guess I can try using an actual piece of wire to left cable as see if the engine idles rough. I tried using my test light (LED) and nothing happened.

@ Cheryl

The DPFE hoses are installed correctly. They are different diameters so it is hard to miss the correct placement.

Ok so I pulled the EGR and Throttle body out. The TB ports are all clear. I cleaned the TB as well. I applied vacuum to the EGR while it was out and I can see the seal opening about 1/8" to 1/4". Mechanically is seems to be working.

I'm starting to suspect if the issue related to the EGR solenoid. Like the signal to the solenoid is not been sent. I have an extra solenoid laying around and swapped it out. I got the same results.

I'm kind of interested to know what the voltage readings are if you put the old sensor back in. Do you happen to still have it?

Tutti57 wrote: I'm kind of interested to know what the voltage readings are if you put the old sensor back in. Do you happen to still have it?

It was pretty much the same readings if you referring to the solenoid. That is the one I switched. I made no difference.

jayta98 wrote: I'm still trying to figure out why did the EVR test failed... I followed the video and nothing happened. I guess I can try using an actual piece of wire to left cable as see if the engine idles rough. I tried using my test light (LED) and nothing happened.

I'm starting to suspect if the issue related to the EGR solenoid. Like the signal to the solenoid is not been sent. I have an extra solenoid laying around and swapped it out. I got the same results.

Really? :blink: We're onto something there. KOEO, what are the voltages on the two EVR wires?

Wiring diagram for reference:



If you happen to have an incandescent test light around, try that one instead, as the LED will never carry enough current to energize that solenoid. If the test light doesn't work, try a jumper wire to ground. Just make certain you're on the brown/pink wire.

Tyler wrote:

jayta98 wrote: I'm still trying to figure out why did the EVR test failed... I followed the video and nothing happened. I guess I can try using an actual piece of wire to left cable as see if the engine idles rough. I tried using my test light (LED) and nothing happened.

I'm starting to suspect if the issue related to the EGR solenoid. Like the signal to the solenoid is not been sent. I have an extra solenoid laying around and swapped it out. I got the same results.

Really? :blink: We're onto something there. KOEO, what are the voltages on the two EVR wires?

Wiring diagram for reference:

If you happen to have an incandescent test light around, try that one instead, as the LED will never carry enough current to energize that solenoid. If the test light doesn't work, try a jumper wire to ground. Just make certain you're on the brown/pink wire.

KOEO with the electrical plug connected to the solenoid I have 12v on each wire. If I unplug the wire connector and measure the voltage I have 12v on the red/yellow wire and the brown/pink is ground.

So if I'm going to use a jumper wire to test the EVR test like showed in the video I'm going to use the jumper wire from battery ground to the brown/pink wire I should see the engine stall a little and the DPFE voltage should increase, correct? I just want to make sure I don't fry my PCM when using the jumper wire. So from battery ground to brown/pink wire? Sorry to ask twice but i want to make sure.

Thanks everyone for stepping in and help. I have this problem for about a year now. I will like to resolve it.