DCT transmission overheat?

[sometorque]

Greetings. I was just doing some stop and go driving in moderate traffic on my way home when for a brief moment this light popped up. It was on and off in about 1-2 seconds.



As mentioned, it seems to be related to the transmission overheating. Car drove perfectly normal afterwards. Just to be sure, I did a few high load pulls on an empty stretch of road and the light did not return. However, this is where it gets interesting.

After arriving home, I took a look under the car to see if I could see any leaks. From what I saw, the undercarriage of the car was leak free. However, after popping the hood, I noticed the coolant reserve tank cap had somehow worked itself loose to the point of being about to fall off. I tightened it down, but it appears to not be sealed against the tank as I remember it being originally (There seems to be a very slight gap between the cap and tank when fully tightened. Pic below for reference) .



I checked under the hood and no signs of leaking coolant anywhere. Not sure if the two issues are somehow related, but it's awfully coincidental that I'd get the light above with the coolant reserve tank cap loose.

Any ideas as to whats going on here? Thanks in advance.

[sometorque]

Update - Just drove it around town for about 30 minutes while applying various amounts of load to the transmission and it drove just fine. Not a single hiccup or hesitation. Also checked the coolant level and it's dead on the max line, which is where it has been since I checked it a month back.

Going to chalk this one up as a fluke, and if it returns, I'll take advantage of the CPO warranty and have the dealer look at it.

[Pissoff]

The dealer can pull the trans code and freeze frame from when it set. I would take it in for them to look at it.

[edisapimp]

Gremlins! Hopefully it doesn't come back.

[sometorque]

Originally Posted by Coleroad

The dealer can pull the trans code and freeze frame from when it set. I would take it in for them to look at it.

I've been dealing with the car randomly throwing lights here and there for the last several weeks, which the dealer is never able to find a code for, so I have a feeling this may be related. Last time I was in for it, they claimed the negative battery cable was frayed. They replaced it, and sent me on my way. Car has been perfect for the last 3 weeks, up until today.

I'm going to monitor for a few days, and if it comes back, bring it in.

[sometorque]

Originally Posted by edisapimp

Gremlins! Hopefully it doesn't come back.

Pretty much, lol. This car has been pretty reliable, minus these little issues.

If it light comes back, i'll bring it to the dealer. Given that it didn't come back after a pretty spirited drive a few hours ago, I have a feeling it may just be a fluke or related to the previous issue i've had of lights randomly coming up for a split second.

[sometorque]

Just a quick update.

I read on the m3 forums of someone who had a similar issue, performed the transmission adaptive reset and never had it pop up again. Tried doing it myself, drove around after for about 30 minutes in 90 degree heat while purposely applying heavy load through the transmission. Added a few hard pulls on some empty backroads as well. I basically beat the car up a bit, and nothing. No lights, no strange noises, nothing that seemed off.

My diagnosis is my car is possesed by the ghost of BMW phantom lights.

[sometorque]

Meh. It popped up again today after a some spirited driving followed by hitting some bad traffic. Came up for about 2-3 seconds and then disappeared. Car drove perfectly normal before, during, and after the light. Did a few hard pulls and the light didn't come back.

To my knowledge, the DCT slips the clutch in low speed driving. Thinking the combo of spirited driving followed by low speed traffic didn't let it cool properly.

Either way, car is still under warranty. Gonna bring it by this week. Will update when I get info.

[sometorque]

Thought I'd update this one.

I took it in on an unrelated issue (Starter took a crap) and had them look at the trans overheat. They were able to pull the codes the two times it happened and after looking at the transmission, found the trans gasket leaking. Had it repaired and all was fine, until today.

Doing some light city driving, it popped back on for a split second and the car kicked up from 7th to 4th gear, presumably to take load off the tranny. I put it in manual mode immediately after and did a bunch of hard pulls in 7th at low speeds to put some load on the tranny and it didn't come back on. The light is completely erratic and it's so quick in duration, I'm starting to think faulty sensor. Going to bring it back in and see whats up.

Real glad it's a CPO car right now, but I'm starting to think i'll be unloading it when the warranty is up.

[sometorque]

Just to update, I'm still dealing with the issue. The warning will pop up every few weeks or so and will flicker on and off a few times. Car starts frantically looking for a higher gear to take load off the transmission when it does this. The car will freak out for 20-30 seconds and then go right back to normal. Otherwise, it drives perfectly normal and no indication of a failing transmission.

The car has been to the dealer 3 times for this, and all they can find is the transmission going into "failsafe mode" based on my driving habits, which is odd given that the car is not driven even remotely hard. They shrugged it off as a normal occurrence and told me not to worry too much about it. No other faults found in the car.

I'm a bit frustrated with this all. While I'm almost certain it's not a catastrophic tranny issue given that i can go weeks or even a month before the warning comes back, it makes me not want to hang onto the car past the warranty. Have a sneaky suspicion there's a software issue at hand here or a bad module. It's going back again this weekend after popping up several times in the last week.

[Downeaster1]

BMW Tech here, your clutches are getting worn out. The temp code isn't fluid temp, it's surface area temp of the disks.

[sometorque]

Originally Posted by Downeaster1

BMW Tech here, your clutches are getting worn out. The temp code isn't fluid temp, it's surface area temp of the disks.

Interesting. I've been reading as much as I can on the dct boxes, and was under the impression that it measured fluid temperature. How do you know it's the clutch discs? I'd be curious to get a more in-depth explanation

Car has 81k miles and I suspect the previous owner did drive it hard. Aside from the trans temp warning every few weeks, it drives fine.

[Downeaster1]

Originally Posted by sometorque

Interesting. I've been reading as much as I can on the dct boxes, and was under the impression that it measured fluid temperature. How do you know it's the clutch discs? I'd be curious to get a more in-depth explanation

Car has 81k miles and I suspect the previous owner did drive it hard. Aside from the trans temp warning every few weeks, it drives fine.

I've disassembled the ones for core return just out of curiosity. There are two disk temp sensors and one fluid temp sensor, but the fluid temp sensor isn't for anything other than being compared to the engine coolant temp for the reason of it holding gears longer when the fluid is cold in order to achieve normal operation temperature sooner.

[sometorque]

Originally Posted by Downeaster1

I've disassembled the ones for core return just out of curiosity. There are two disk temp sensors and one fluid temp sensor, but the fluid temp sensor isn't for anything other than being compared to the engine coolant temp for the reason of it holding gears longer when the fluid is cold in order to achieve normal operation temperature sooner.

Interesting. Thanks for sharing.

From what I've scraped together online in research, there's an actual specific code for a clutch pack overheat. From what the tech has told me every time I've brought the car back, its just a generic code based on my "driving profile" and not a specific fault of the transmission.

I guess my question is; if it was the clutch packs failing and overheating, wouldn't there be a specific code triggered by one of the clutch pack temp sensors?

[Downeaster1]

Originally Posted by sometorque

Interesting. Thanks for sharing.

From what I've scraped together online in research, there's an actual specific code for a clutch pack overheat. From what the tech has told me every time I've brought the car back, its just a generic code based on my "driving profile".

I guess my question is; if it was the clutch packs failing and overheating, wouldn't there be a specific code triggered by one of the clutch pack temp sensors?

There is, but that's a mechatronics fault and is unrelated to disk temp faults.

[sometorque]

Originally Posted by Downeaster1

There is, but that's a mechatronics fault and is unrelated to disk temp faults.

Thanks for your insight. Glad to actually be getting closer to a root cause.

I guess my next question is; if the discs are failing, would I see a specific clutch disc temp code or will it just go into a general protect mode?

To note, I haven't once notice slippage. There's also been times that I drive the car very hard without fault. Ironically, the only times the light has turned on is on the highway or in traffic situations. Repeated hard pulls never trigger it.

Thanks for the feedback.

[Mr Rooty Von Tooty]

The DCT is a mechanical gear box with two clutches shifted by a computer, and it is subject to the same wear that an otherwise normal MT would. The first thing to check is the fluid level. It might even be a good idea to drain it to examine the fluid for color and particles of metal or clutch material.

Next like a MT, if you drive the car hard, you can expect accelerated wear of the clutch. In a MT, it is a simple matter to replace the clutch, but in the DCT, it is probably a very expensive proposition?

In any case, I have never had to replace a clutch, and I don't intend to in the DCT. I drive it with that idea in mind.

[sometorque]

Originally Posted by Mr Rooty Von Tooty

The DCT is a mechanical gear box with two clutches shifted by a computer, and it is subject to the same wear that an otherwise normal MT would. The first thing to check is the fluid level. It might even be a good idea to drain it to examine the fluid for color and particles of metal or clutch material.

Next like a MT, if you drive the car hard, you can expect accelerated wear of the clutch. In a MT, it is a simple matter to replace the clutch, but in the DCT, it is probably a very expensive proposition?

In any case, I have never had to replace a clutch, and I don't intend to in the DCT. I drive it with that idea in mind.

First thought was the fluid a few months back.

When the issue first popped up, the dealer found a leaky trans pan and replaced the pan, new fluid and new pan gasket. Unfortunately, the issue remains.

I had thought clutch packs as well, but the irregularity of the issue and the fact that there is not a hint of slippage from the clutches in any gear makes me think there's something else amiss here. I've had the light come on before the car is even halfway warmed up cruising on the highway and then no warning after a half dozen hard launches after an hour of driving in 90 degree weather. It's completely inconsistent without rhyme or reason.

I spoke with the previous owner, who informed me the car was never tracked and while reflashed at one point, wasn't beat on any more than most of us would drive these cars. Given that the car came with a nice stack of maintenance records, I'm inclined to think it was reasonably well-cared for.

I've been chatting with downeaster and the shop foreman at the local BMW dealership here and they're both leaning towards one or both temp sensors being bad or a software issue. According to downeaster, the temp sensor is not a serviceable item, which makes me wonder if this means a new tranny or not.

We'll see. It's going back to the dealer tomorrow.

[dtla1]

Thanks for the updates. I'm curious to hear the outcome as I drive my car spiritedly, but I'm always worried that I'll be left with some sort of catastrophic fault.

[Gangplank]

Following.

[HyeWarrior]

Also sub'd

[sometorque]

Originally Posted by dtla1

Thanks for the updates. I'm curious to hear the outcome as I drive my car spiritedly, but I'm always worried that I'll be left with some sort of catastrophic fault.

Originally Posted by Gangplank

Following.

Originally Posted by HyeWarrior

Also sub'd

Will be updating with my findings. Purpose for me documenting this in detail was the unique nature of the issue and the fact that my car has a good bit miles more than most (81k and climbing), so this may be an issue others may soon face as these cars start climbing in mileage. To note, I spoke with the tech the day they replaced the leaking trans pan and filled with fresh fluid and he informed me the fluid came out in pretty good shape without any indication of any trans components failing. I have a sample I saved that I'm going to finally get around to sending to Blackstone for analysis.

Car is under CPO warranty for another 7 months, so I'm hoping a final solution is found before then. Given that the car drives normal 90% of the time, I suspect I'm dealing with either a software bug or a bad sensor, but I'll let the techs at the dealer make the determination. I wouldn't let this thread detract you from driving your car spiritedly. This is a BMW and not giving it a good flogging from time to time is almost criminal lol