2013 Mustang GT transmission issue?

Hey everyone, today my 2013 mustang gt with 98k miles and the automatic 6r80 transmission had an alarming transmission issue.

The car has been sitting for a little over 2 weeks in my apartments parking lot with much of that time spent covered in snow and ice. I went out today and cleared all the car off and dug around the wheels and behind the car so i’d be able to get out. The battery was dead so I jumped it using my daily driver explorer.

Car started after a jump no problem at all and ran/idled smoothly. I waited for 2 or 3 minutes for the car to idle and allow all the fluids to circulate. I then proceeded to put the car in reverse to back it out of the parking space and felt and heard an EXTREMELY hard CLUNK. I was a little surprised since it had never done this before, so I put it in park and then once again shifted into reverse to feel the exact same very hard clunk once more. I backed out of the space, put it in drive (noticed there was no clunk when going from reverse to drive) and began driving down the road. The first thing I noticed was that the car wouldn’t shift out of 1st gear. Or maybe it was 2nd gear I don’t remember. Either way, the rpms kept going up and up but the car wouldn’t shift into the next gear. I thought maybe the car had gotten locked into a gear by accident (although I don’t think this is possible if the car is in regular “D” mode) but nonetheless I shifted the shifter down into sport mode because when you do this it will display what gear the car is in on the gauge cluster display screen. Well when I put it in sport mode nothing showed up on the screen, like the car didn’t even recognize it had been shifted to sport mode. The screen didn’t display anything either when I pressed the upshift/downshift buttons on the shifter while shifted into sport mode. Just nothing.

I pulled into the closest parking lot and parked, shifting into reverse one more time just to confirm what I dreaded, feeling the extremely hard clunk once more. I just sat there thinking about where to call for a new transmission, then put the car in park and shut it off.

A couple minutes later I decided I should try to limp it home since I was still pretty close and when I turned it back on and shifted into reverse it shifted COMPLETELY normal. No clunk whatsoever not even in the slightest. Smooth as can be. I tried putting it in park again, then reverse once more and again, absolutely not even the slightest clunk. I then tried shifting to sport mode and the display screen lit up saying “SPORT SHIFT MODE” then when i pressed the up/downshift that’s on the gear selector it cycled through all the gears on the screen. I then proceeded to drive the car and now it drove completely normally shifting through all the gears 100% fine no slipping no delayed shifts, when before it was refusing to shift at all. VERY strange.

I have an OBD tuning device that tells me trans temperatures and the temp has never gotten above 190 in all 18k miles of my time of ownership including today. I am positive there are no leaks in the trans because I would have seen fluid all over the ground from being parked for so long, not to mention would have smelled it and also the temps would be through the roof if the fluid was so critically low that the car wasn’t shifting or having problems reversing.

I’ve never had any transmission issues before with this car and it certainly had never done that before ever. I got the car at 80k miles and first thing I did was change the trans fluid and filter myself, original fluid came out dark red NOT brown or black, then I drove it for a few thousand miles and got a second drain and fill and filter change done at the dealership just to make sure the most of the old fluid was gone and the new fluid was as clean as possible. Now 18k miles later absolutely no trans problems until now.

Could what I described be the beginning of the end for my transmission? to me the problem almost certainly seems like something electrical since the trans went from working 100% the last time it was driven 2 weeks ago to 25% and then back to 100% within the span of a few minutes. Can someone share insight about what could have caused this and if I should be worried?

I have a few theories. Can someone tell me which, if any of them, are the most likely to be correct? Or something different entirely?

1.) it was pretty cold outside (33 degrees or so) and maybe the fluid wasn’t circulating properly since it was very cold outside and the car had not been started in 2 weeks, however I waited 3 minutes after starting the car before putting it into gear plus i’ve driven it in way colder temps before without issue so I highly doubt this is the cause.

2.) maybe some snow got stuck in the u joint on the driveshaft and this prevented the car from shifting or being able to recognize twhat gear the car was in? However if this were the case wouldn’t the car not move at all then?

3.) I have a trans tune from VMP performance to optimize shift points. Maybe since the battery died some of the computers parameters got reset, while still thinking it was on the trans tune, however this makes no sense because the tune stays loaded onto the ECU so theoretically it should override any factory parameters that would be reset if battery was disconnected

4.) the car is very low to the ground. Maybe some sensor in the trans got wet from snow being under the car and sitting there for so long causing damage and then when I turned on the car things began to warm up, drying out the sensor causing it to act erratically when the car was still cold but then fixing itself when the car was turned off and back on with everything also being warmed up.

5.) there is a serious internal transmission issue that appeared out of nowhere and I will need a rebuild soon. Despite my fluid being clean and full and me rarely beating on the car and when i do so, i make 100% sure it’s at full operating temperature. Also trans was working perfectly fine 2 weeks ago when I last drove the car and never had an issue before

6.) a fluke that has no reasonable explanation

Any help appreciated

When that happens, many things can happen with the cars computers and modules to where it takes time to relearn operating parameters again.

Drive the car, and if it operates normally, attribute it to that.




I’ve experienced slightly strange shifting in other vehicles before from the battery being disconnected but they’d all shift through the gears smoothly, just the shift timing was different but that’s because the learned shift points were forgotten from battery being off and now the car had just reverted to factory shift points. And the shifts themselves still felt smooth and normal for the most part.

I’ve never owned a car that wouldn’t shift out of gear though and clunk very hard in reverse (when the vehicle never did that before) just from the battery being off though and then seemingly fix itself just from simply restarting the car.

Also I’ve actually replaced the battery on this mustang about a year ago since the old one died and the transmission did not act like this after replacing the battery plus I’ve had the battery off doing maintenance or repairs numerous times and nothing like this ever.

However that was before the car was tuned and I’m not going to rule it out and honestly at this point it seems like the only logical explanation. That or the trans or some sensor in the trans is beginning to fail.

  1. Yes cold could be an issue…
  2. Not likely, the car can overcome any ice with the 1600 ft-lbs or so the car can transmit in 1st gear.
  3. Probably not
  4. The sensors are all IN the trans… and THAT could be causing your problem. There are 3 sensors, I think, all molded into a “lead frame”. Two speed sensors and one temp sensor. If the cold affected one of the two speed sensors, the trans goes into limp home and sets it to 2nd gear. Unless you are running down the highway and then is locks it into 5th gear. If the speedo stopped working, it was the output speed sensor. If the speedo was working it is likely the shaft speed sensor and that will cause limp mode, too. These are all connected through the trans case through a big round plug on the passenger side of the trans. You could have gotten moisture in there and cause the problem.
  5. Not exactly serious… although the lead frame ($160) has been on back order for months. I had to replace mine but I had to buy an entire solenoid valve pack and lead frame assembly for $550 or so. You MUST return the tune to stock so the valve body can be calibrated to the PCM. Then you can put your tune back in. The rest of the 6R80 is a tough transmission, so not likely anything else is going bad.
  6. I laid out reasonable explanations… BUT it could still be a fluke (the ice, the cold, failing sensor…). Keep driving and see if it happens again. If it does, notice if the speedo works. Your OBD reader (or better yet, ForScan) should be able to run data on all 3 sensors. If either input or output sensors are zero, you know what you need to repalce.
1 Like

Thanks for that info. I will try doing another cold start tomorrow and see if the trans acts up again. If everythings normal next time then is it safe to say it was just a fluke? But if it happens again on the next cold start and then improves when warm or when turning the car off and on, there’s a pattern and number 5.) would seem like the most probable.

On a similar note, when those sensors inside the trans you mentioned begin to fail are they usually temperature dependent when showing symptoms of failure such as delayed or no shifting and hard clunking in reverse? In other words would they normally only show those signs of failure when everything is cold and then improve when warmed up or restarted?

Also I had my sct obd tuner plugged in and could see trans temp readings on the device so that eliminates the temperature sensor going bad correct? I might try to take it to a shop tomorrow and see if they can scan for input and output trans sensor values. What should the values be reading at if they’re working properly?

The trans operations does not depend on the temp sensor as much as the other 2. Your speedometer is fed by one sensor so no speedo, no sensor. The 3rd will cause limp home.

My output sensor failed over several months. Usually when the trans was warm. I don’t live where it gets cold so I can’t say what happens. It would act up and then come back just like yours did.

I wouldn’t bother have the sensors read, they will show OK. When the trans acts up then they won’t show OK. I managed to capture the data with ForeScan that showed the output shaft sensor dropping the signal.

Good ideas above. From my diy’er perspective, hard to say w/any certainty, but your guess of an electrical system problem makes a lot of sense. It could be related to the jump start, not something I’d recommend for newer cars. I’d say you’ve taken a prudent course so far. Suggestions:

  • If the battery is dead again, recharge with a shop battery charger overnight at a slow (e.g. 2 amp) charge rate, rather than attempting a jump start. If you absolutely must recharge your battery using another vehicle, disconnect your car’s battery first , then charge it while it is disconnected from your car, using the other vehicle. If you also can’t disconnect the battery for some reason but still need a recharge, then at least leave your car completely “off” while recharging.

  • I have an older Ford C4 automatic trans which exhibits similar symptoms to those you report above if the vacuum modulator(s) get disconnected. Yours probably doesn’t use vacuum modulators, but your symptoms would be consistent if the transmission’s solenoid-operated control valves (the electronic version of vacuum modulators) were not being placed in the correct configuration by the drivetrain and/or transmission controller, again consistent w/an electrical problem of some sort.

For anyone that cares I did another cold start today and drove it for an hour and didn’t have anymore issues.

I think it was acting up just because of the dead battery. I found a forum where several other people with the same car as me experienced the same types of transmission problems after their battery died and was solved by simply turning the car off and back on.

1 Like

Late to the party but FWIW, my first thought was battery discharge. And I don’t know any specifics on this vehicle, but sometimes problems come not just from forgetting learned settings, but also from various computer modules not being supplied adequate voltage on start up. Whole different story, but Toyota Prius are notorious for having weird, unpredictable disappearing problems if their 12V batteries are too low on voltage at start up. (Ask me how I know…)

Also FWIW, if that battery is only a year old, and it didn’t have enough juice after 2 weeks, then you might want to look for a parasitic draw. Sure, 2 weeks in cold weather might be enough either way. But if that battery is only a year old, even with cold temps, it should still be able to start the car unless something is drawing it down.

In addition, if you find a discharged battery, and if you’re not in a pinch for time, it is 100% better overall to put the battery on a charger to bring it up to full charge rather than using a jump start. Jump starting is obviously a necessity at times, but is also alternator abuse. The alternator is meant to run the electricals while the car is running and keep the battery topped off. But it’s not a battery charger, and asking it to be one is not healthy for it.

Finally, I saw that your fluid had been changed and that there are no signs of leaks. I also saw that things seem to be good now with trans operation. But I didn’t see (tho I may have missed it) that you have actually checked the fluid for proper level. Two weeks of drip down, cold fluid (tho I know that you did run it for a bit), makes for the possibility of low fluid symptoms like hard shifting. I don’t think it’s likely, but best to just verify the fluid level.

Mostly I hope it keeps working well for you.

Unfortunately the transmission fluid is a pita to check in 05 and up mustangs. For one, it requires a jack and jackstands to get under the car to access the dipstick and they could not have put the dipstick in a more inconvenient location - about 2 inches away from the exhaust pipe! Also the trans needs to be at an exact temp i believe 90-110 degrees f to get an accurate reading.

On a similar note, I haven’t bothered checking the fluid level because the dealership did the 2nd drain and fill/filter replacement 6 months ago and trans temps never went above mid 190s. So I assumed the level was correct not only because the dealership did it but because i’d imagine the trans would overheat (I believe ford says normal operating temp for a 6r80 is as hot as 205 degrees) but I never saw the temp go over 195 ever and most of the time it was lower.

Would it be accurate to say that if the trans fluid was underfilled and/or too old or dirty that the trans would almost certainly run hot? (In this case temps would read over 205 on the scanner). Or in other words, as long as trans temps are reading within normal range (in this case between 190-205) then would it be safe to assume that the fluid is probably fine, in terms of both condition and level?

Not just exhaust the passengers side catalytic convertor!

185 actually. The trans has a thermostat that sends fluid to the front mounter cooler at 185 and above. It takes some driving to get it there.

No, to all of these.

Again, no.

If the trans starts slipping or the convertor won’t lock up, the temps will increase.

I recently track tested 2 tunes and the stock settings at a track day in my '14 Mustang GT. The tunes produced higher peak fluid temps than the stock tune (224 vs 212). I suspect that they left the convertor un-locked for longer for the torque multiplication it provides and that creates more heat.

I really really hate that. And have experience with it myself as my SAAB 9-3 is the same - tho luckily not near the exhaust! If it was me I’d still go through the trouble to check it, but if it is “behaving” itself now, then you might also just see what happens for a while. (And to echo Mustangman - don’t take trans temp as telling you anything about the fluid).

I know this is an old thread but i was about to change the transmission fluid today. I have done it before myself when I first got the vehicle, fluid was very dark after the first drain and fill so I am doing another drain and fill now, a little over a year later to ensure (almost) all of fluid is new. I had a few questions:

1.) Does the tranny have to be warmed up when i drop the pan to drain the fluid or can i do it cold?

2.) Will less fluid come out if i drain it cold vs draining it hot

Cold is fine and what comes out should be the same. The manual says how much should come out with a pad drop but I got more out of mine than the manual said.

That’s good. I am doing it on jackstands so if i am going to have to take a bath in transmission fluid i would at least rather have it be cold than scorching hot

Best investment for removing transmission pans… lol
Parts stores/amazon have them and they fit on top of most drain pans…

Don’t remove all the pan bolts and then knock then pan loose, leave a couple in one end of the pan about 2 turns from finger tight before loosing the pan from the transmission, when done correctly, not much mess…


1 Like