Code P0401 troubleshooting

2002 MERCURY MOUNTAINEER
120,000 MILES • 4.0L • V6 • 4WD • AUTOMATIC
Avatar
LAWRENCE CHENOWETH
  • MEMBER
  • 39 POSTS
Trying to troubleshoot this thing slowly. all the vacuum lines are off and even the red and green hard lines are off and don't understand the diagram. there is solid lines and dotted lines need to know where they go please. Someone took it apart and I wasn't around. Now trying to figure it all out again. It was idling bad to where it wouldn't stay running. Would a bad EVAP canister cause that or any good ideas? it's been a good truck.
Oct 26, 2019 at 3:49 AM
Advertisement
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
Good morning.

The code is for the DPFE sensor. It is a feedback sensor for the EGR system.

The hoses are easy. They are different sizes and cannot be placed in the wrong position. The electrical connector is the only connector.

This sensor is the most common failure for this code.

If the hoses melted from heat, then that is different. If that is the case, that indicates a clogged catalytic converter.

Roy
Images (Click to enlarge)
Attached Media
Attached Media
Oct 26, 2019 at 4:39 AM
Avatar
LAWRENCE CHENOWETH
  • MEMBER
  • 39 POSTS
Would this happen to be the one?
Image (Click to enlarge)
Attached Media
Oct 26, 2019 at 4:47 AM
Advertisement
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
Correct.

Roy
Oct 26, 2019 at 4:52 AM
Avatar
LAWRENCE CHENOWETH
  • MEMBER
  • 39 POSTS
Is there a way to test it because it's only about a year old? How about a way to test the EVAP canister purge valve? out of all the things that go wrong with this system what is usually the number one cause? please and thank you.
Oct 26, 2019 at 5:00 AM
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
Okay, first, the EVAP has no connection to the issue you have with the code.

Yes, the most common is the sensor itself. To test it, you need an advanced scan tool to read the signal voltage being sent back to the PCM.

Do you have a real scan tool that can read live data?

Roy
Oct 26, 2019 at 5:04 AM
Avatar
LAWRENCE CHENOWETH
  • MEMBER
  • 39 POSTS
It won't run long enough for that.
Oct 26, 2019 at 5:05 AM
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
Okay, so there is another issue. You did not state that in the original post. Are there any other codes?

Have you checked the fuel pressure? That is where I would start. The sensor will not cause this issue at all.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Roy
Oct 26, 2019 at 5:11 AM
Avatar
LAWRENCE CHENOWETH
  • MEMBER
  • 39 POSTS
Ya, I'll have to check that because it runs rough and not very long. I'll do that thank you.
Oct 26, 2019 at 5:14 AM
Avatar
ASEMASTER6371
  • CERTIFIED EXPERT
  • 52,796 POSTS
You are welcome.

Keep us updated.

Roy
Oct 26, 2019 at 5:15 AM