SpectreH

My '13 GT has develpoped an issue. While cruising down the road, something is causing the speedometer to lose its signal. When this happens, the car will downshift to match the spped it thinks the car is going. It was real fun in rush hour traffic going 70 MPH and the car downshifting to 2nd.
Anyhow, suspecting a bad OSS (Output shafte Speed Sensor), I took the car to a highly recommended transmission shop. They looked it over and pulled three codes: U-3000-4, U-0401-68, and U-0401-81. They said the transmission itself was fine and did not charge me for their time.
I talked to a friend who is a mechanic, and he said some possile problems are diode bad in alternator, causing a ripple in the voltage that can cause weird stuff, wet SJB (it is nice and dry, never had a leak there), or the main computer going out.

Any other suggestions? I can pull the alternator and have it tested. He said he has seen them charge fine with a bad diode but wreak havoc on the CAN bus.

houtex

https://www.dtcdecode.com/Ford/U3000-04 - Unknown error type. Something happened, but it doesn't know what.

https://www.dtcdecode.com/Ford/U0401-68 - The module is reporting something it depends on is not correct. External issue.

https://www.dtcdecode.com/Ford/U0401-81 - Bad data happening.

So he's right. There's some communications/electrical wonkityness going on here.The alternator check is a good idea, as well as any grounds and also ensure your battery terminals are clean clean clean and slathered with dielectric grease, and using battery washers. Also apply dielectric grease to all alternator connections. Then you're just checking wiring for either bad/corroded/melted connectors and/or chafing somewhere.

Electrical/comm gremlins are SO fun. You might need a shop with probes and scan tools, not a transmission guy for this one, as this is pointing to a 'car' problem overall.

SpectreH

Thank you. Yes, the transmission guy, who was highly recommended from a friend of mine who works for Ford, said this was out of his area. I thought it was nice that he did not charge me for his time. I cna check connections, battery terminals, and alternator. If that does pan out, I'll send it to the shop. I'm just glad I'm the one it malfunctioned on. Not knocking my wife, but I'm not sure how she would have handled the rear wheels essentially locking up at 70 in traffic.

SpectreH

Update: I checked the connectors to the computer, all seemed ok.
The battery terminals were another story. Positive was nice and clean, and at a glance, the negaive had just a little. However, upon disconnecting and inspecting, the negaive had quite a bit inside and underneath. I cleaned it nicely with wire brushes on the Dremel, installed the felt washers and lots of dielectric grease. A 10 mile test drive went well yesterday, and the trip to work this morning as well. The real test will be the ride home since the problem showed up more when it is hot out. Here's to hoping the expense was just the few bucks for grease and washers. If it still acts up, my next step will be an alternator test.

SpectreH

Update 2: Everything went well for the ride home. I took back roads to avoid the interstate in case of another uninteneded high speed downshift. If today and tomorrow go well, I think I'll mark this one as fixed.

houtex

Good to hear!

SpectreH

Another update: The problem has come back. After inspecting connections and having the alternator and battery tested, I started looking online for more ideas. It seems the F-150 and some 2011-12 Mustangs with the 6R80 transmission are being recalled for this problem. I filed a complaint with the NHSTA so my VIN would be in the list of complaints and dropped the car off at Ford Tuesday after work. I gave the the codes that were pulled earlier, just in case my disconnecting the battery cleared them. Apparently, there is a faulty lead frame in the transmission. This is the first time I have ever had the dealer fix a problem outside of the airbags and a few minor warranty items, so I hope it goes well. If it wasn’t for the prospect of Ford one day reimbursing me if the recall expands, I might have just installed a new or reman 6r80 myself. I don’t trust shops very much.

SpectreH

Final (hopefully) update: I got the car back yesterday. New fluid, filter, pan gasket, lead frame, connector. There is a 2 year, unlimited mileage waranty on their work. Fingers crossed that all is now well in my Mustang world.

crjackson

@SpectreH

Normally I wouldn’t post to a thread this old, but did you last entry close this out? I’m having the same U0401-81 on my 2014 Premium GT. I have an MT82 however. Ford told me to just ignore the code because it means nothing. I have an issue whereby occasionally, my car will stall upon coming to a stop (like an older car with a bad dashpot). I can’t help but think the two issues are related.

A friend of mine believes it’s the tune that causes the stalling issue and unrelated to the code. The stalling issue appeared after some shop-installed Roush Phase 3 SC / headers / calling system upgrades. It’s starting to get on my last nerve... The (well known/ regarded) Dyno Tuner has no clue why it would randomly stall, and he defends that it’s not the tune.

Thoughts?

SpectreH

I my issues are fixed as indicated above. In you ocase, I would think tune, or possibly a dirty throttle body. I had a stalling issue that was cured by cleaning the throttle body.

crjackson

Thanks, mine has a new Roush TB, Intake, MAF. All clean, all brand new. Less than 3k miles. I guess I'll go back and argue with the Tune shop some more. I can't make the U0401-81 code go away permanently though, so I thought perhaps it's related.

houtex

His solution won't solve yours. The manual and the automatic share no commonality of parts, so all what was done on his wouldn't apply to yours.

Now... as to the stall (code later), it's a manual transmission. Unless you're riding the clutch all the way down to a stop (which I know you're not doing) there's very little that the manual transmission can do to cause the car to stall. Of course, if the clutch is NOT fully disengaging, that could be the entire source of the stall. Easiest thing to do is from a stop, put it in first, and keep the clutch in, on a level playing field, and see if the car rolls along with the clutch in. If it does, you need to investigate why the clutch is still engaged. And/or if the MT-82 has somehow gotten it's gears locked in with the input shaft, but I seriously doubt it's in the transmission. That'd be a pretty catastrophic event if that was the case.

Electrically/computer wise, there's only three (3) connections to the transmission: Neutral safety switch, reverse indicator for lamps, and the speed sensor. And while they *might* be giving you that code, that's probably a harness issue, and/or the computer might throw a *specific* code for the sensor in question. The code you're seeing is an ECU/BCU one, as in the instrument cluster isn't passing through the information between the body and the engine.

So I don't think it's the transmission. I'm fairly sure we can rule that entire beast out.

Therefore the engine is the problem. And therefore the ECM is *potentially* the problem. And therefore the tune is *potentially* the problem. The code you're getting may have something to do with it, or may be it, but you can read about that later. The point being, though, that as long as all things are equal, when you're coming to a stop, the clutch is in, the transmission is in neutral... the engine should just come back down to idle and stay there.

There's quite a list of thing to check, though. Any of which could be it, or a combo thereto...

I'm going to mention engine mounts and transmission mounts. Although it's *highly* unlikely... perhaps they're somehow causing an unwanted shift due to wearing out, and maybe that is causing a problem what makes the engine stall. Perhaps a fuel line gets pinched and causes a lean condition. Perhaps an electrical connector gets pulled taut and causes loss of signal. All kinds of things like that. Again, highly unlikely, but throwing it out to see if it sticks.

Speaking of shifting, well, inspect *all the things*, wiring, fuel, etc. Anything that might not like a forward shift. Or any shifting. Could just be a loose this or that, and it doesn't like slowing down and gets petulant.

Fuel filter. It's changed and good, right?

Fuel pump. You have good fuel pressure, right?

Fuel. It's good stuff, right?

Fuel tank: It's not gunked up, right?

Injectors. We know they're fine?

Spark plugs and coil packs. All good in the hood, right?

A/C on or off? They are different maps in the ECU.

That's an EPAS car, no power steering pump, so wheel turning doesn't matter...

Alternator is good? Low output could cause it. Mods such as stupid-fire-hellapower amps and subs? Maybe remove those from the load... check the battery? It's good, no corrosion on terminals, all grounds are good and not rusted or such?

Then we get into... not much else. I highly doubt the crank is shifting forward in the block causing frictional drag and stalling the engine. Not impossible the thrust bearing is shot, but you'd think there'd be one heck of a racket goin' on too. One assumes you have the right weight, type, and amount of oil, yes? Yes, of course, silly of me to even mention... But have you changed it regularly, and with quality oil and filter? Again, silly of me, how very droll, my extreme not-good, please to excuse.

And after all that... well, that leaves the ECU being unhappy. As in the idle return circuit/map/programming is wrong. That'll really require a tuner to tune that out. But it'd also require a tuner what's receptive to doing so, and it sounds like you've got the wrong guy. He should *want* to fix that, even if it's free, because his/his company's reputation is on the line. If it turns out that everything else is eliminated and it's down to the tune still, that means he (siphons greatly with a large amount of negative pressure) and you can be sure *I* don't want to buy from and/or work with him, because I know what I'm not getting: good service after the sale.

(inner monologue proceeds...of course, all that said with vitriol due to face value of your post, and context is important, so maybe dial it back, houtex... Ok... Sorry... just... that's what it looks like, me, so... yeah. I'm kinda ticked... I need to get over it, don't I? Yes, I do. Ok.(end inner monologue)

Not sure what else can cause it after all that mess. So get to work, you got things to look at.

---

On the code, I found this tidbit on them thar intarwebs, what I didn't find last time...
So maybe it's one of those, the engine oil temp and/or inlet air temp. If they're on the same harness and side of the engine that might be an indicator.

I also found this annoying voiced video, but it's very interesting information. and specifically for THIS particular code:
So that's what all those code things mean... cool.
If you skip to about 3:00ish, it says the problem lies in the *ABS* module, specifically the left front wheel speed sensor... which is interesting, how's that related to emissions...?
And yet, I'm inclined to believe this one. The ABS module is the problem, or the sensor on the left front wheel is, or the wiring thereto. Reason I believe is that they have other videos for Ford on the U0401:xx codes, all different end results. This makes this more plausible to be right than not, to me.

Which brings me to the dealership you *seem* to have mentioned... you did say 'Ford' anyway... The dealership that you went to is sus because they said 'ignore it'. I may want to report that to Ford corporate if I were you, or at the very least insist on a nice meeting with the service manager and/or GM and have them *detail to you* exactly what a U0401:81 is. Because you need that figured out. If it's the ABS, then that's a problem you don't want getting worse. And at the end of it, it's something the tuner can say "see? Fix it!", because the ECM does talk to the ABS module. If it's getting wonky data, it *might* cause the tune to go stupid and stall you out. You did get charged a diagnostic fee for that right? Right. Get your full fee's worth, get the paperwork from the shop manual that says specifically 'You can safely ignore this, it will cause NO ISSUES WHATSOEVER, we swear, we're Ford, and we'd NEVER lie to you.' Maybe not in so many words, but still.

Overall, yeah, can o' worms and lots of possibles. Not sure what else to say except good luck, and hope I helped even a little with it!

/I can't seem to find the subcode decoder. And it looks like each manufacturer gets to play with it, so... yeah. You may need a Ford Dealership Shop Manual (equivalent) what has that available to ya. If anyone knows where/how to get that online, well, here's a good thread to remind/show us.
//Thatssa lot. But I'm home ill, so why not type stuff...

crjackson

Okay, so I didn’t want to hijack this thread, but I’m going to add some context here for better understanding ...

I know this has nothing to do with my transmission, clutch engagement/disengagement problems, oil or oil changes, battery/alternator.

When the car stalls, it’s about once every month and half at the moment. The car is rolling, clutch is disengaged, and transmission is already in neutral. When I’m rolling up to a light, I generally slip into neutral, and coast to the light. I don’t like to sit at long lights with my foot on the clutch for various reasons (TOB wear, Thrust Bearing wear, lazy, etc...). The idle will drop down quickly and the engine will shut off while still rolling. It’s like it has a carburetor and the throttle valve is snapping closed with a bad dashpot that allows it to close too rapidly.

The car has 40k miles, never a problem, very well maintained.

Throttle body is new / clean. As is the TPS, manifold, Roush CAI, Roush S/C, Ford 47lb injectors, plugs, radiator, fan, heat exchanger, Kooks LT headers, OPG/CS, and various other things. All have about 3k miles since the install. This is when the issue developed.

I didn’t have the ability to scan for universal codes before now, so I don’t know if the U code was present before the install/upgrades, but I kind of doubt it.

Yes, I took the car to a Ford Dealership that has the regional Ford trained tech. That does all the service/repairs/diagnosis for the Ford GT’s in the region. That cost me $327.00 ... I’ll explain why in a minute...

After the install, when I noticed it started having the stalling issue two weeks later. I started checking for codes (I have 4 different scanners). The car had both permanent and pending Cam Position Sensor codes. I thought this was the source of my stalling. I took the car back to the installer/tuner and they had it for 3 days with no luck finding the source. I took my car home and headed over to my regular Ford dealer and had a candid talk with them about weather or not they could address those codes. The service manager told me they had the regional Ford GT tech working out of their dealership that day, and he went to talk to him. He came back and said he would find and fix the problem without hesitation. They made me an appointment for the following week.

I took the car in, and 30 minutes after they put it in a stall, the service writer came to the waiting room and handed me a damaged connector for the Crankshaft Position Sensor. He told me that this was the source of the Cam Position sensor codes. 20 minutes later, I was paying the bill and all OBDII codes (that I couldn’t clear previously) both permanent and pending were gone. However, when I got home and checked, the U code was still there. I called Ford and spoke with the service writer. He in turn spoke to the tech. who advised I could simply clear that code and forget about it. They told me if it returns, I can just ignore it because it’s insignificant and may come and go over the life of the car.

Even though I had a hard time believing this, I accepted their word since the other codes were gone and the car was running great. Since the car seemed to never stall afterwards, I assumed this problem was solved.

Fast forward to today. The stalling returned. Granted, it only did it once, I’m very familiar with this and pay close attention when it happens. It’s the same problem as before as far as stalling is concerned, but no codes (except the U code). It hasn’t happened in cool weather until now. It generally happens when ambient temperature is above 80º F based on previous observations. In warm weather, it will happen about once a week (after the SC install, but before the connector repair at Ford).

Understand that, at all other times, this car idles and runs much smoother than stock since the SC Install / Dyno Tune. It’s as smooth as butter, but when coming to a rolling stop in neutral or with clutch fully disengaged, it will occasionally drop to 0 RPMs instead of stopping at 750-800 RPMs. It just drops all the way down and stalls.

It never throws a CEL, it doesn’t produce any OBDII codes, and runs like new in all other instances. I have a friend who who races this exact model car and SC. He swears I’m chasing a tune problem that’s not likely related to the U code. He is several hundred miles away, so I can't rely on his hands-on help.

I wonder if it could be related to the Roush CAI and included MAF sensor. I know they also have to add a 2nd sensor for IAT2 and that required some re-pinning of one of the connectors.

I don’t have the skill or physical ability to work on this myself, so I’ll have to pay someone to fix this unless the tuner can rework the tune to eliminate the issue.. Thus far, I’m not feeling confident in their abilities to diagnose and fix the issue.

There you have the full story, and I have fully hijacked this thread. My apologies to you @SpectreH .

SpectreH

No problem with the hijack. We’re here to help each other. I wish I had more to offer.

awoychosky123

Add one more person to the U0401-81 code problem, its the only code that comes up on my 2013 5.0 motor with the MT-82. When I clear it with IDS it stays gone till the next key cycle. No clue what is causing it, harness was damaged in one spot but it was related to power steering and has been fixed. Abs module is used and from the donor car, So im not sure if replacing the ABS module with a new one and reprogramming it will fix it or not, Last time I had a bad abs module I had dash lights that wouldnt go away no matter what...So Im thinking the problem must be elsewhere. Just not sure where, If anyone every ends up fixing their U0401-81 please update us. There is a thread on SVTperformance but there's not much in the thread. Some information my donor engine had a CAI that was removed and replaced with a factory airbox, however Using IDS I flashed the PCM back to stock as I did not have access to the tuner used to tune the PCM. So I should be running OEM specs on my PCM. Also I'm pretty sure IDS shows this code on the IPC not the PCM.

crjackson

Yeah, my scan tool shows it as IPC code as well. If I ever find a solution, I’ll post it here and on the SVT thread.