U0401 HELP! 2012!

Dsaline · Dec 26, 2018

I have a 2012 F-350 that will intermittently get a U0401 code which will cause a service advancetrac light and a reduced engine power display. It will then start my truck out in 5th gear with no option to put it in manual. What could this possibly be? thanks!

BigRed97 · Dec 27, 2018

Check the bus wires near and in the connector over the left front fender well.

Dsaline · Dec 27, 2018

I have, even pulled them out and cleaned them all. Went about 3 weeks before it popped up again.

rrkroll · Jan 1, 2019

There is another bus type connector attached to the e-brake bracket under the dash. I would pull that apart and clean. If you use the e brake much I would also detach the plug from the brake bracket

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TitoF250 · Tuesday at 3:48 PM

Dsaline said:
I have, even pulled them out and cleaned them all. Went about 3 weeks before it popped up again.

Did you solve the issue? I'm having the same problem...

keith.ciolkosz · Wednesday at 7:30 PM

I have a similar problem with my 2011, although I do believe I found the problem, and the symptoms were a little more advanced. I would have ABS light come on Traction control light, check engine light, would also flash engine over temp and reduced power on my dash as well as the wrench indicator, also stuck in 5th. At times I could manually shift next time nothing worked. Also symptoms would just disappear which took a little digging to find.

Just waiting on a new part before I can 100% confirm.

Curious if you figured out the issue on your truck?

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TitoF250 · Thursday at 12:24 PM

keith.ciolkosz said:
I have a similar problem with my 2011, although I do believe I found the problem, and the symptoms were a little more advanced. I would have ABS light come on Traction control light, check engine light, would also flash engine over temp and reduced power on my dash as well as the wrench indicator, also stuck in 5th. At times I could manually shift next time nothing worked. Also symptoms would just disappear which took a little digging to find.

Just waiting on a new part before I can 100% confirm.

Curious if you figured out the issue on your truck?

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What part did you order?
The shop just called and said replacing a 20amp fuse with a 30amp fixes the issue. They are going to continue to look into that circuit.

keith.ciolkosz · Thursday at 8:11 PM

TitoF250 said:
What part did you order?
The shop just called and said replacing a 20amp fuse with a 30amp fixes the issue. They are going to continue to look into that circuit.

Huh, what fuse are they talking about?

The part I ordered was the portion of wiring harness communicating to my TCM I found a bad connector, the connector that was bad was the one that sits above my drivers side fender well, right underneath the power distribution box. Not saying that’s your issue but that’s where I tracked mine to.

I was losing intermittent communication between my PCM and TCM causing all the weird symptoms.

I suppose I could have just changed out the connector, but the harness was cheap enough and less messing around on my end I figured.

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TitoF250 · Friday at 8:25 AM

keith.ciolkosz said:
Huh, what fuse are they talking about?

The part I ordered was the portion of wiring harness communicating to my TCM I found a bad connector, the connector that was bad was the one that sits above my drivers side fender well, right underneath the power distribution box. Not saying that’s your issue but that’s where I tracked mine to.

I was losing intermittent communication between my PCM and TCM causing all the weird symptoms.

I suppose I could have just changed out the connector, but the harness was cheap enough and less messing around on my end I figured.

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I believe it was the fuse feeding the PCM or ECM. I'm going in to pickup my truck today so I'll know a bit more.
The said they found the issue. Apparently, my air compressor that is powered from upfitter switch #1 has gone bad. They removed it from the truck and all the symptoms have gone away. I have a hard time believing that could cause all of these issues if the switch was off when the problem happened.

I figured it'd be a connector/wiring harness issue like you had found. Could you post a photo of that connector? Also do you have the part #?

keith.ciolkosz · 2024-08-05T19:05:53-0400

TitoF250 said:
I believe it was the fuse feeding the PCM or ECM. I'm going in to pickup my truck today so I'll know a bit more.
The said they found the issue. Apparently, my air compressor that is powered from upfitter switch #1 has gone bad. They removed it from the truck and all the symptoms have gone away. I have a hard time believing that could cause all of these issues if the switch was off when the problem happened.

I figured it'd be a connector/wiring harness issue like you had found. Could you post a photo of that connector? Also do you have the part #?

This is the connector that is causing me the issue. Hopefully this helps you out. If not there are a number of other things that can cause the same issue I learned just from punching in my issues into YouTube.

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